Thinking of starting USA game

I am thinking of starting a US game as I have never played American before. Can anyone advise on league structure, cups etc as I am not sure??

Is it worth playing?, are there any continental cups, i.e an equivelant to the champions league? If there are, who is that against??

Thanks

We have a guide to the MLS here. Anything else, you shoud ask on chat if you want a quick answere because I barely know anything about the MLS.