in addition to what's described above, ESo is weird in that you don't get abilities unlocked autimaticaly as you level. you have to deliberately level skill lines from which you want abilities, but typicaly picking up the first available ability and placing it on your active bar. as you gain experience, so do your skill lines, which in turn unlocks more of that skill line where you can put your skill points into other abilities. if its sounds confusing, that's only half because of my being terrible at explaining things. the other half is honestly the game itself
you do indeed eventually get a rotation, but at early levels, your skill bar is mishmash of more or less random stuff that's only there to let you eventually pick up abilities that ARE good and are going to be part of your eventual rotation.
and rotation in this game is key. you can go through a lot of content just spamming right mouse button. but anything at end game, especially vet difficulty? good rotation far more so then gear - will make, or break you.