Multiple GAW user accounts can be created on a single device (phone or tablet) and each user account has an associated e-mail address and password. Multiple accounts can have the same e-mail address. Each user account can join multiple servers, and you can join the same server up to 3 times with different user accounts . When a server is joined, a new commander must be made with a name that is unique to that server (which could be different from the user account name which must be globally unique).
Warning: when joining a server it is possible to leave the commander name blank. If you do this, a random name will be assigned to you (something like s1234567 with random numbers) and it is currently impossible to have this name changed! 
Bookmarks are stored as cache data on a device, rather than the usual server-side storing, as such they can be lost when uninstalling the Galaxy at War Online app. Commander's bookmarks are also stored seperately for each sever (even several commanders on the same server don't share their bookmarks).