There are two type of tourneys now. Arena style and the normal Swiss. There are fewer of the latter than there used to be but they still exist.
https://support.chess.com/customer/en/portal/articles/1444927-how-do-live-tournaments-work-where-can-i-join-one-
That explains the difference in formats and also lists the schedules for the events.
I have recently transferred to the current chess.com site from the old site where I enjoyed playing in tournaments,.I don`t understand the new site much and when it comes to tournaments, well it`s nothing like a chess tournament, a player can come and go at will and it sure does not resemble anything i have seen in over the board chess.Now am i missing something or is this the new so called tournaments