1. Motherboards
Motherboard Basics

2. Form Factors
Motherboards are available in several form factors, which essentially unify the design of certain aspects of the computer system.
The most common form factor is ATX.
The form factor of the motherboard affects both the power supply and the case design.

3. Expansion Ports
Motherboards have a variety of expansion ports built into them. These expansion ports are designed to accept specific formats of expansion, or adapter cards.
Today, common expansion ports are PCI, PCI Express, and AGP.
AGP is quickly being replaced by PCI Express.

4. Onboard Components
Motherboards vary in the number and quality of onboard (built-in) components.
Certain onboard components, such as Audio and Video devices, are generally lower performing than adapter cards which are installed in expansion slots.

5. A Typical ATX Motherboard

6. A Micro ATX Motherboard Notice that it has fewer expansion slots.

7. Understanding
Be sure to familiarize yourself with the different styles of motherboards available as well as popular features and reliable manufacturers.
Reading reviews of products is an excellent method of researching before you make purchasing decisions.