It depends on your licensing setup and what you want to restrict.
If you wish to restrict how many people access it you can restrict the number of document CAL's assigned to the application (on the documents>user documents menu fo the QEMC)
Obviousley anyone with a named CAL will be able to access any documents that have been distributed to them
If you wish to restrict who accesses it, you can specify that in the distribution options under docments>userdocuments then edit the properties of your document.
You can also specify access to indidivudal sheets dependant on windows login by having a conditional show of
Edit: also on the User documents sectiopn (under concurrency) of the QEMC you have a limit to maximum concurrent session per document
When you say server do you mean the Qlikview Publisher server, i.e. do your users access the application via their browsers?
If so then I'm not understanding your license model, users need to use eitehr:
In all cases, If you logon on to the QV Managment Console, choose the documents tab, then source documents, choose your chocuments, clik edit from the right hand side, then go to distribute and only choose the users you want to access the published application.