Since the keyboard and mouse you're installing are wireless, they can not receive power from the computer like wired keyboards and mice can which is why they require batteries. Turn the keyboard and mouse over and remove the battery compartment covers. Insert new batteries in the directions shown (match + with the + on the battery and visa-a-versa).
Place the keyboard and mouse wherever comfortable on your desk. Please keep in mind proper ergonomics when deciding where to position your new equipment. Making the correct decision now can help prevent carpal tunnel syndrome and tendonitis in the future.
Note: If you have an existing keyboard and mouse that you're using during this setup process, just move them elsewhere on your desk until this setup is complete.