Well it is upto you where to start. But you have to start from the Admin panel but decide yourself where to start depending upon your requirement. If your super admin also falls under the user permissions (user management) then you can directly start from managing the users first then go for rest.
It seems you are going to ask the whole project here. I think no one is going to tell you the complete database structure here. Forum is not to ask the whole business ideas and code for whole site, use it as a helping hand when you get stuck technically somewhere them come here.
But lets see if someone is going to give you a complete table and their structures. BTW, why don’t you search in google before you re-invent the wheel yourself. I think you will a huge list of results in google if you search “PHP Image Gallery”.