My iPhone applications aren't working what should i do?

Your apps that came pre-installed on the iphone, mail, iPod, calendar, etc., should work anyway. If even these apps don't work, you have a software issue and need to first try rebooting the phone, if that doesn't help connect to iTunes and restore phone to factory settings, should take care of the problem. You can restore settings using the phone too in general settings, but do it through itunes so it backs up your phone first. Otherwise you may lose information on your phone.