You really should get a reseller involved that can help you and knows how the product works and is implemented. They are also well versed in the licensing of the product.
By the sounds of it, you are new to BackupExec (even though it's been out for more than 10 years.)
When you download the trial, it is everything. It'll work in trial mode with whatever agents you choose to enable at the time of installation. If you do not put in a license key, the feature/option will work for 60 days, then expire. It can only be re-enabled with a purchased license key.
The product is also licensed with a lot of options.. You have the base Backup Exec install, tape drive licenses, virtual agents, application agents, server agents, archiving options, deduplication, etc...
Again it's best you get a reseller to walk you through the licensing, even better is to find a local reseller that can do the sale and the installation for you.