When you click on the "online giving" link, you will be taken to a different page. If you are a first time user, you will need to set up an account. You do that by clicking the person head in the upper right hand corner. You will need to fill out some information and then you will be good to go.
To log back in...go to "log in", it will show a sign up screen again. If you already have an account, the log in is just below the sign up button.