Entry level question but…

I have recently started my first job as the network admin for a company. The owner wants to limit who can and can not use the internet. I keep thinking there is a way to do this through permissions in AD but can’t seem to remember how. If anyone could tell me how to allow/deny internet use on specific computers/users it would be greatly appreciated. The company has approximately 50 computers and is using active directory on Windows Server 2003 Enterprise Edition. Thanks in advance.