Cant llink my gmail acount to my ipad 3? please help

Are you using the Gmail app, or do you mean something else?

There are some instructions here.

Have you gone to your settings and added this? If not go to settings -> Mail, Contacts, Calendars -> Add Account -> Gmail. You'll be prompted for your email address & password (Can also name Gmail account if you have multiple ones). Now when you use the mail app on home screen (Unless you moved it to a different page) you should see a Gmail folder. Hope this helps.