When you make a donation to a campaign, you must check this box when you donate in order for your name to appear publicly on the campaign page.
Please note that while you can choose to prevent your name from showing visibly on the campaign's list of supporters, the project team will still have a record of your donation amount and associated email account.
If you want to be more anonymous, you can create a StartSomeGood profile with the name Anonymous, and use an email account that you still check (so you can receive updates about the campaign), but that is not obviously connected to you.