
MurphysParadox |

There are two parts to this.
1) Using the staff's spells: A staff is a spell trigger item, and as such can only be used to cast spells that appear on the list of spells your class can cast. So the wizard could use it for Finger Of Death, but not for Heal. You would treat casting Heal from the staff as if it were a wand for the UMD check.
2) Recharging the staff: So long as at least 1 spell on the staff is in the user's spell list, you may recharge the staff. To recharge, you expend one spell slot equal to the level of the highest level spell on the staff (regardless of the spell list). In this case, Finger of Death is the highest level spell (7th), so the wizard would have to drop one of this 7th level spells per day casting to give 1 charge to the staff.
If the user was a cleric, he'd only be able to use the staff to cast Heal, but he'd still have to expend a 7th level spell to charge the staff because that's the highest spell level on the staff.