Coordinating conjunctions (and, but, so, because)

and (addition)
but (contrast)
so (result)
because (reason)

And (addition):

I bought apples and oranges.

But (contrast):

He is tired, but he keeps working.

So (result):

It was raining, so we stayed home.

Because (reason):

I was late because the bus was delayed.

And vs But

And connects similar ideas; but introduces contrast.

So vs Because

So introduces a result; because introduces a cause.