Hi there and welcome to the community.
If you could try texting the word "settings" to 2020,you should receive your "settings" via a text message.
If that doesnt work for you,and you have access to wifi,then there are two apps,that can be found,in your google play store.
Either install the giffgaff APN app or Tweakker.
Either of these apps,should fix your "settings" for you automatically.
If you would like to go to your google play store and get the giffgaff APN app,simply click onto the link below.http://play.google.com/store/apps/details?id=com.qmusa.giffgaffapp
If you would like to try tweakker,click onto the link below.http://play.google.com/store/apps/details?id=com.tweakker
To set your "settings"manually.
Go to "settings"
Wireless and networks.
Access point names.
Tap the menu key.
Select new APN.
(Type in this information).
press the menu key,then SAVE apn.
Tick the apn to see the green light,you now should be set up for internet and mms.
Ensure your data is enabled or use packet data.
Then turn your device OFF and On again.