You buy it and when DLCs are released, go to the store on the in game menu and download the DLCs from there. Make sure to note though: the season pass does not include micro-transactions such as the wolf skin.
Just make sure that you access your DLC downloads from the in game store. You will still have to pay if you go through the PSN store through the main XMB menu.
If you go through the in game store, all the prices for these DLC should show as free when they become available. This is what you want.