AND It is used to join two similar ideas together. The subject can be omitted when it is the same as in the previous sentence. Ex: He was born in London and (he) has lived there all his life.

BUT It is used to join two contrasting ideas. Ex: My father is Spanish, but my mother is French. The subject can also be omitted if it is the same as in the previous sentence. Ex :I like the cinema, but don´t often go.

OR It is used to join two alternative ideas. Ex: I can lend you my dictionary, or you can buy one. When the subject is the same in both sentences we can omit it. Ex: I’d like to watch a film or listen to music.

SO It is used to show that the second idea is the result of the first. Ex: The boy was very tired, so he went straight to bed. We don´t omit the subject in the second sentence even if it is the same as in the previous one.

BECAUSE It is used to give the reason of something. Ex : We didn’t go swimming because the water was dirty. We can use because at the beginning. Ex: Because the water was dirty, we didn’t go swimming.