They will equip the best items from what you give them, but make sure it suits their class.
Always give your followers some good equipment (For their class).However, some quests allow additional followers to join you temporarily. You can have one human and one animal follower at all times.Here is the list of followers you can find in Skyrim. Once you complete that task, they will join you for good. Most followers have a task you must accomplish before they join you.
They fight with you, carry your things, and stay loyal to you no matter what. In Skyrim, followers (or companions) are more usable than ever before.
