Great idea! Get in touch with the cause (non-profit organisation) and have them apply for a GivenGain cause account. Once their cause account is activated and they have set up their cause profile, you'll be able to raise funds for one of their campaigns.
When the cause is set up and ready, click on "Start fundraising" on the campaign page of their cause profile and set up your activist project. Use the PDF below to guide you. Good luck!