A supporting or sub-campaign is a campaign that is directly below a main campaign. Donations from a supporting or sub-campaign will benefit the main campaigns goal.
Here is an example: If JILL created a campaign and JACK wanted to support JILL's campaign, JACK could go to JILL's campaign page, click the JOIN THE TEAM button, and create his own campaign page. Every dollar raised from JACK's campaign page will add to JILL's fundraising goal. JACK's campaign page will also show up in the OUR SUPPORTERS section of JILL's page.