Hi MissJessieAnn,
Check all of your Home screens to see if it accidently got moved. You cannot delete iTunes from your phone, so it is there somewhere. If you don't find it then:
Reset your phone (nothing will be lost): Hold down the Home and Power buttons at the same time and continue to hold them down until the Silver Apple appears. Once the Home screen redisplays, see if your iTunes icon is back.
If it is not, check Settings>Restrictions, and make sure that Restrictions are on. If they are on, make sure that iTunes Store is set to = On under the "Allow" section.
If that is not it, then swipe down from the center of your screen and do a spotlight search for iTunes. If the spotlight search finds it, see if it is in a folder (it will say the folder name next to it if it is).
Finally, if all else fails, you can go to Settings>Reset>Reset Home Screen Layout to get all of your icons to go back to their original settings. That should make your iTunes ap show up on the first Home screen.
Once you get your icon back, if you are not able get the iTunes store to stay open from the iTunes icon, then try to open the Store from the Music icon.
Cheers,
GB