In other words, the basic interface and controls in Champions operate and feel like those in most MMOs you may have played. One interesting aspect that reminded me of my very brief experience with Cryptic's last comic book-themed MMO, City of Heroes, was an auto-attack ability (in this case, a basic ice blast) bound to the first ability slot. Toggling this ability on would make my character attack the targeted enemy repeatedly, which in turn filled up a special meter below my character's health bar. Once that meter was full, it activated some of my stronger and snazzier powers mapped further down the ability bar.
What I saw of the PVP setup in Champions was fully consensual. You activate it by hitting the PVP icon on your interface, which pops up a browser that searches and lists all the currently open PVP matches. Then you hop into one of those--which seem to be instanced, since you get a loading screen and are then transported to an arena separate from the game world--and start laying it down against other players. A Cryptic rep told me some of these PVP matches would tie into quest storylines and requirements, though you're also free to just jump in and start blasting characters on the other faction to relieve stress if you want.
The company also released a wealth of new media showing off Champions' PVP aspect; take a look at this trailer for a better idea of how this stuff is going to work.