To use items, go to the 'Games' icon (the ball and the bat). Then, scroll down to 'Items' and scroll through your items to see what one you want to use. Although, most items can't be used until your Tama is an adult.
To sent presents, go to the 'Connect' icon (the heart) on both Tamas. Then (still do the same thing with both of the Tamas), when it says 'Playmate?', click Ver. 2. Then, choose 'Present'. When you see the 'Stand By' screen on both of the Tamas, press the B button on the Tamagotchi that you want to give the present to.