A Server license (one per copy of Windows Server 20XX)
Service User or Device CALS (most of the time people get user CALs) you would need one per each user accessing resources from servers on your network.
RDS User CALs (again one per connection) so if you have 10 people accessing RDS but only 5 ever connect at a time you can get just 5 CALs
Once you have the RDS CALs you would deploy a RDS licensing server (if you only have one server you can install the role on there)
Import your RDS CALs into the licensing manager
In your RDS configuration you would tell it which licensing server to use.