Hi,
Sorry for the noob question, but I just can't figure out how to use the spells that come with the items like ring of mage armour or the wog collar. How do I use the spells?

Personal suggestion, read the descriptions well and stay wary of items with charges that self-destroy upon use. If they haven't fixed this for IWD2, you should still be able to sell and buy limited charges items to recharge them though.