Operation Hydra offers three completely new gameplay modes that will be subjected to small changes throughout the course of the event. The new modes introduce certain additions to the staple team vs. team gameplay. These features are free of charge. Interestingly enough, all three modes are subjected to a week-long rotation (each mode is available for one week, then gets switched to a different one, and so on) you can view the details of each mode below.
Check how to play in three different modes in CS: GO Operation Hydra: