You can add people after the group is created by going into the group page and clicking on the members tab.
You will then see an invite button on the right hand side of the page. Click this.
You'll then be prompted to enter an existing GoConqr username or enter their email address directly. You can invite both existing and non existing users. You can enter a message as well telling your friend about the group.
The list of invited friends appears at the end of the "Invite member" pop-up window.