In a nutshell:
Tier 0 - You own the account completely. Not shared or loaned.
Tier 1 - Shared loaned account, no expiry, use own account to play the game
Tier 1.1 - Same as Tier 1 above but can be used only for 6 months.
Tier 2 - Shared loaned account, no expiry, use the account given to play the game.
Tier 2.1 - Same as Tier 2 above but can be used only for 6 months.
I give you a new psn account, you download the game from this account. After you started the download, you log off to your own account and wait for it to finish downloading, then you can play it using your own account.
You can re- download the games within 6 months of purchase on the same PS3, after that you can't. However the game will be still playable forever on your PS3.