For standard English, you should use a comma before 'and' and 'but' when they joing two complete sentences.
I cleaned the garage, and my brother helped.
I cleaned the garage and mowed the lawn.
I wanted to go to the movies, but my wife wanted to stay home.
I wanted to go to themovies but was too tired.
Some styles use a comma in front of because, but some do not. Here in the US, a lot of newspapers put a comma before because. However, in academic writing, the comma is not used.