If you have access to wifi then download the giffgaffAPN app from the market and run with option 2. This will sort out your internet and MMS settings.
Otherwise you can do this manually by following this http://bit.ly/giffgaffandroid - Android guide
If its just a nomal phone nothing fancy text: settings 2020
If its an android phone
or downoad GiffgaffAPN from android market
And if its an iphone: