Because, so, although and but

Because-porque; So-por lo que; Although-aunque; But-pero.

Use because to express a reason.
She was driving fast because she was in a hurry.

Use so to express a result.
She was in a hurry so she was driving fast.

Use although and but to show a contrast. Although can go at the beginning or in the middle of the sentence.
It was late but she couldn't sleep.
Although she tried to stop, she hit the man.
She couldn't sleep although it was late.