Hi,As your phone is an android based phone you maybe able to use an app from the play store to install the giffgaff APN settings ,see the link below
Or you could install an android giffgaff app
here's the offical giffgaff app
If that doesn't work on your phone then
you could look to see the internet settings for most androids here and add them manually to your phone
Go to Settings.
Choose More Settings.
Choose Mobile networks.
Choose Access Point Names.
Press the Menu button on your phone and choose New APN.
Tap Name and type giffgaff, then tap OK.
Tap APN and type giffgaff.com then tap OK.
Tap MMSC and type http://mmsc.mediamessaging.co.uk:8002
Tap MMS proxy and type 188.8.131.52
Tap MMS port and type 8080
some devices (4.2 & above ) may need more settings
MVNO type: IMSI
MVNO value: 23410x
APN protocol : IPv4
APN Roaming protocol : IPv4
Now press the Menu button on your phone again, and choose Save.
Tap the little circle to the right of the profile named giffgaff on the list. It should turn Green or Blue
Your phone is now set up for giffgaff's internet and MMS settings.