Let's do these in order of easiness.
To add users, you must have a workgroup defined. Search this forum for "securing a database" to see what is involved.
In the main (or "database") window, using the MENU bar, there is path
Tools >> Security >> Add Users and Groups >> a dialog box that lets you add users and groups.
OK... adding an ICON to a form? Why? (I.e. what do you wish to do with it?) That's NOT a rhetorical question. Your answer will tell us the direction in which to point you.