can not get internet tried the APN app but will not save ???
If you are referring to the 'giffgaffAPN' app, that won't work with Anndroid Jellybean which is used by the Nexus 7. I'm not certain that the 'Tweakker' app will work either, since it sends the settings via SMS which I don't think the Nexus can do.
Your best bet would be to create the APN manually.