If I give my magic weapons and enchanted rings and amulets to my followers, will they use it? If not how do i make them use it?

Also, can followers use potions and poisons if I give it to them ie. give an archer follower loads of ravage health potions, will he use it on his arrows?

I've read that followers will use healing potions sometimes, but not poisons. Only certain enchantments take effect for them. Here's a list of those enchantments: http://www.uesp.net/wiki/Skyrim:Followers#Enchanted_Follower_Equipment

You can use the Fortify Armor enchantments to get them to wear armor that is not in their major skill, as long as the math works out.