FTX.com offers derivatives and spot markets, but does not serve USA residents.
FTX were unhappy that they could not offer services to American users so they created the FTX.US platform.
FTX.US supports ACH deposits, serves USA customers adhering strictly to the US regulations - as such, it can't offer derivatives such as the popular BULL and BEAR leveraged tokens but it make up for this by having margin trading available, with up to 10x for qualified users.
Please note, residents in the states of Washington or New York (and possibly other states) are not permitted to create accounts at FTX.US
Canadians and European users can use either FTX.com, FTX.US or both sites.