Your SAS Account team should be able to help you with these questions.
Prime workloads are mission critical/production workloads. Non-Prime are more adhoc in nature.
Session Type - ETL, Analtyics, Reporting, ...
Concurrent Sessions - how many total workloads (SAS sessions) will be running at any given time.
Average Input Data Volume per SAS Session - what is the size of the data - on average - that will be used by your concurrent sessions.
Again, if you do not know the answers to these questions, please work with your SAS Account team.