When you pick a shroud and enter monster form, you get a special AA window with two tabs.
The right hand tab is inherant monster abilities. If you pick a wizard it will have 3 "spells", Fire, Frost and Thunder which are your nukes. Mostly you can't spend any points here, they are just set according to the level of the monster. The three nukes for example will be at Level/5, so picking a level 60 wizard will show fire at 12/12.
The left hand tab is to customize your monster. You'll get an amount of unspent monster AA points to use here, the amount doesn't seem to follow a set formula, the 60 skel wizard I picked got 91 for example. On this tab are the basic player AA's for raising stats plus a selection of ones based on your monster. The skel wizard can select ones to increase fire, cold or magic (thunder) damage, mana regen, mana preservation, spell crits, etc. Warriors get a mix of melee ones like combat fury and the like.
On the right are load and save buttons. Once you pick and are happy you can save the set, then when you pick that monster again you can just hit "load" rather than select them all again.
Spells are not spells in that they don't go on the spellbar, they go on your hot button menu. Part of the reason for giving us 4 hot bar tabs now.