Here are the rules for buying and keeping items.
1. You may only have 3 Items. You should post them in your Profile so that people can see it. When you use the item (If it has uses) you lose it and must delete it from your Profile.
2. You can do one of the 2. Create your own page for purchases, or you can post in the items store.
3. You cannot buy items while in a battle. You can only buy them before or after.