How Do I Sync My Iphone To My Computer After I Have Already Connected It To Itunes

I just got an iPhone yesterday and I connected it to iTunes. I don't think I have set it up properly, or maybe forgot to click something, because I am unable to carry apps over that I have downloaded to my phone because I am not authorized on this computer. Is there anything to do? If I have to restore the phone, how do I back it up and then put the backed up data back on my phone? Thanks!