1. Composition

2. About compositions
A composition is the framework for a movie. Each composition has its own timeline. A typical composition includes multiple layers that represent components such as video and audio footage items, animated text and vector graphics, still images, and lights.
You add a footage item to a composition by creating a layer for which the footage item is the source. You then arrange layers within a composition in space and time, and composite using transparency features to determine which parts of underlying layers show through the layers stacked on top of them.

3. About compositions
A composition in After Effects is similar to a movie clip in Flash Professional or a sequence in Premiere Pro.
You render a composition to create the frames of a final output movie, which is encoded and exported to any number of formats. Simple projects may include only one composition; complex projects may include hundreds of compositions to organize large amounts of footage or many effects.
In some places in the After Effects user interface, composition is abbreviated as comp

4. About compositions
Each composition has an entry in the Project panel. Double-click a composition entry in the Project panel to open the composition in its own Timeline panel. To select a composition in the Project panel, right-click (Windows) or Control-click (Mac OS) in the Composition panel or Timeline panel for the composition and choose Reveal Composition In Project from the context menu.

5. About compositions
Use the Composition panel to preview a composition and modify its contents manually. The Composition panel contains the composition frame and a pasteboard area outside the frame that you can use to move layers into and out of the composition frame.
The offstage extents of layers—the portions not in the composition frame—are shown as rectangular outlines. Only the area inside the composition frame is rendered for previews and final output.
The composition frame in the Composition panel in After Effects is similar to the Stage in Flash Professional.

6. About compositions
When working with a complex project, you may find it easiest to organize the project by nestingcompositions—putting one or more compositions into another composition. You can create a composition from any number of layers by precomposing them. If you are finished modifying some layers of your composition, you can precompose those layers and then pre-render the precomposition, replacing it with a rendered movie

7. Create a composition
You can change composition settings at any time. However, it’s best to specify settings such as frame aspect ratio and frame size when you create the composition, with your final output in mind. Because After Effects bases certain calculations on these composition settings, changing them late in your workflow can affect your final output.

8. Create a composition and manually set composition settings
Choose Composition > New Composition, or press Ctrl+N (Windows) or Command+N (Mac OS).

9. Create a composition from a single footage item
Drag the footage item to the Create A New Composition button
at the bottom of the Project panel or choose File > New Comp From Selection.
Composition settings, including frame size (width and height) and pixel aspect ratio, are automatically set to match the characteristics of the footage item.

10. Create a single composition from multiple footage items
1-Select footage items in the Project panel 2-Drag the selected footage items to the Create A New Composition button at the bottom of the Project panel, or choose File > New Comp From Selection 3-Select Single Composition and other settings in the New Composition From Selection dialog box:

11. Create a single composition from multiple footage items
Use Dimensions From
-Choose the footage item from which the new composition gets composition settings, including frame size (width and height) and pixel aspect ratio.
Still Duration
-The duration for the still images being added.
Add To Render Queue
-Add the new composition to the render queue.
Sequence Layers, Overlap, Duration, and Transition
-Arrange the layers in a sequence, optionally overlap them in time, set the duration of the transitions, and choose a transition type

12. Create multiple compositions from multiple footage items
1-Select footage items in the Project panel
2-Drag the selected footage items to the Create A New Composition button
 at the bottom of the Project panel, or choose File > New Comp From Selection
3-Select Multiple Compositions and other settings in the New Composition From Selection dialog box:
Still Duration
-The duration of the compositions created from still images.
Add To Render Queue
-Add the new compositions to the render queue

13. Duplicate a composition
Select the composition in the Project panel.
Choose Edit > Duplicate or press Ctrl+D (Windows) or Command+D (Mac OS)

14. Timeline panel
Each composition has its own Timeline panel. You use the Timeline panel to perform many tasks, such as animating layer properties, arranging layers in time, and setting blending modes. The layers at the bottom of the layer stacking order in the Timeline panel are rendered first and—in the case of 2D image layers— appear farthest back in the Composition panel and in the final composite.
-note
To cycle forward through Timeline panels, press Alt+Shift+period (.) (Windows) or Option+Shift+period (.) (Mac OS). To cycle backward through Timeline panels, press Alt+Shift+comma (,) (Windows) or Option+Shift+comma (,) (Mac OS)

15. Timeline panel
The current time for a composition is indicated by the current-time indicator (CTI), the vertical red line in the time graph. The current time for a composition also appears in the current time display in the upper-left corner of the Timeline panel
The left side of the Timeline panel consists of columns of controls for layers. The right side of the Timeline panel—the time graph—contains a time ruler, markers, keyframes, expressions, duration bars for layers (in layer bar mode), and the Graph Editor (in Graph Editor mode)

17. Composition settings
You can enter composition settings manually, or you can use composition settings presets to automatically set frame size (width and height), pixel aspect ratio, and frame rate for many common output formats. You can also create and save your own custom composition settings presets for later use. Resolution, Start Timecode (or Start Frame), Duration, and Advanced composition settings are not saved with composition settings presets.
Note:
The limit for composition duration is three hours. You can use footage items longer than three hours, but time after three hours does not display correctly. The maximum composition size is 30,000x30,000 pixels. A 30,000x30,000 8-bpc image requires approximately 3.5 GB; your maximum composition size may be less, depending on your operating system and available RAM

18. Basic composition settings
Start Timecode or Start Frame
-Timecode or frame number assigned to the first frame of the composition. This value does not affect rendering; it merely specifies where to start counting from.
Background Color
-Use the color swatch or eyedropper to pick a composition background color.
note: When you add one composition to another (nesting), the background color of the containing composition is preserved, and the background of the nested composition becomes transparent. To preserve the background color of the nested composition, create a solid-color layer to use as a background layer in the nested composition