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Yes, it is:
He walked across the room and sat down.
Here, we wouldn't use a comma, but if there's a full clause after the conjunction, we can:
I tried my best, and in the end I managed to do it.
In lists, some people put a comma after the last item but one before 'and', though others don't.
When do I use them? Is it correct to use tem before “and” or “because”?
I know to use them after names.
I agree with Tdol about "and". Unless a sentence is very complex, we don't use a comma before a clause that begins with "because". We would use a comma after a beginning clause that starts with because.
Using Commas 
Linear Mode
