I started playing again after 5 years off. My new player keeps finding these cloaks that cant be used till level 30. they say things like 750,000/1,000,000exp on them.

What are they and what do you do with them?

The 750,000/1,000,000exp is a display that tells you what the target exp is, and how much of that exp goal you've fulfilled. Once you've reached the goal, the item gains a level and increases in effectiveness. Cloaks are a new addition to the game (as of the October patch), but the ability to level items was introduced in the 10th anniversary patch when the developers revamped portions of the "rare" system.

Extensive information on cloaks can be found here: http://ac.turbine.com/index.php?option=com_content&view=article&id=670-cloaks&catid=85-2011&Itemid=68

Good luck.

thanks