The basic gist is that when you hit select to bring up the character window you have three panes, and you use the bumpers move between them. Within a pane, the triggers or D-pad will move you to the next tab left or right. D-Pad left or right will compare an item in your inventory to your current equipped item of the same type.
To bind a spell, I think you need to be on the skill-tree page. Hover over the skill and hit X to select a button for it (Y, A, or Left Trigger as possible slots). If you picked up a spell as loot, you need to highlight it from your inventory to "learn" it first, and then you can bind it to a button from the skill tree page. To teach your pet a spell, don't "learn" it from your inventory, but swap it into your pet's pouch first and then learn it.
And be sure to change your pet's posture (hit start from within the character menus). I go with aggressive for the most part because i like to hang back and do all kinds of spellish stuff.
Last bit is sockets. Some items have sockets you can embed gems into, with each gem having its own set of bonuses depending upon whether you socket it in a weapon or armor piece. You can use the two dudes in town to either a: break down the weapon to recover the gem for re-use, or break down the gems that you have currently slotted in an item to place different gems instead.
I know most people here know most or all of this, but this might help somebody new. I still have yet to mess with multiple skill configurations yet, but it looks like there is a way to swap different button bindings quickly during play. I only wish they had the same feature for equipped weapons and/or armor.
Yeah, the pet handling was a great idea. Having him run to town to sell stuff is awesome. I send him out whenever I go fishing ;P