Not exactly new to Munchkin, but...

[Mister Ed]

You can carry any number of items (as long as you have no more than one Big item). You can only USE one Headgear, one Footgear, one Armor, and two Hands worth of Hand items. Any items that you CAN'T use, for whatever reason, are turned sideways to indicate this. So you could carry three Headgear, but two would HAVE to be turned sideways. Only one could be used at a time.

The relevant portion of the rules:

...you may also use only one Headgear, one suit of armor, one pair of footgear, and 2 "1Hand" items (or one "2 Hands" item)...unless you have a card that lets you ignore these limits. If you are carrying two Headgear cards, for instance, only one of them can help you. You should indicate items that can't help you, or extras not being worn, by turning the cards sideways.