There's an option you have to check in the menu, which allows you to put any skill in any slot, helps massively.
Changed abit since D2 bud, when you start cracking through it you will realise how the skill levels work, skills just become available when you reach the right level.
Not like D2 where you put all your points into hammers for Paladin etc.. The new system makes it so you don't have to re-roll, just adjust gear for a new build