To collect donations through your group, you first need to enter your payment details through the 'Payment Settings' page in the 'Payments' menu on your management toolbar.
For more information on 'Payment Settings', click here.
Adding a 'Donate' tab
Click 'Tabs' in the 'Website' menu on your management toolbar.
On this page you will see a number of options for tabs you can add (more info on those here). Simply drag the 'Donate' box to the left to make it available for your members to see and save the changes.
As long as your payment settings are set already, your 'Donate' tab will appear in the tabs menu of your group.