Equipment is used to aid your character in one way or another with different items doing different things inherently, otherwise it is allowed to have a singular ability/function per item.
Weapons: Increase the strength attribute
Armor: Increases the endurance attribute
Support Items: Increase the Speed attribute
Medical Items: can be used to heal the user.
Each type of item comes with its own generalities, such as weapons always take the form of a weapon of some sort, swords, clubs, guns, ect… Armor takes the form of various body coverings or shields, Support is generally something meant to help you get around with more ease and medical items take the form of healing pills, shots or other healing related things.
Prices are based on the ability the item has. General run of the mill type items will cost 100 Yen while usually the upper tier items will cost 5,000+ Yen. This is based on item abilities. If the ability is unusually powerful, it may be subject to a higher price.