Items in game can be divided easily into two categories: Ground and Space.
Ground items can be equipped or used by either yourself or your Bridge Officers. To equip items on yourself, hit "u", select your name, then find the option where you can equip items, then drag and drop items into appropriate slots. To equip items on your Bridge Officers, click on the Bridge Officer you would like to add equipment to, then drag and drop it on them. Hypos and other usable items can be given to Bridge Officers as well. If you hit "i", your inventory will pop up and you can view all items that you have available for use.
Ground items can be broken up into the following subcategories: