Tableau Server license keys are generally only assigned to one user - the Tableau Server Administrator. If you have Customer Portal access you should be able to log in and view this information. As far as the differences between the "100" and "5" - this is likely referring to how many interactor seats are available on the license key and defines how many users can be granted access to Tableau Server. The links below may help to provide some more background on assigning site roles to users which will use up the interactor seats - as well as how to add the keys to Tableau Server.
Let me know if this helps to answer your question!