Hi DARTrider
All content shown for beta test is free for you to access during the beta test period. The idea here is that creators can have as many people as possible testing their DLC packs during the beta test period. Generally each beta test runs for 2 weeks, and then the creator will either need to resolve any reported issues (if any are reported), or submit the DLC pack for release.
The DLC pack will install like any other DLC pack through the Content Store in TRS19, but will be under the name 'betatest:###' (where ### is the ID number of the DLC pack).
There is no requirement to beta test everything. I think most creators would appreciate as many people as possible testing there content, but if it's not of interest to you (or it's not something you feel you could appropriately test) then that's fine as well.
The amount of content available for beta test will vary, as it depends on when creators mark their DLC pack as being ready for beta test.
Once released, you will need to purchase the DLC pack (or if you have a silver or gold membership subscription, you would need to claim it through here).
Regards