The Borderlands 2 Season Pass includes four all-new add-on campaigns featuring new areas to explore, new adventures to undertake, new enemies to overcome and the Ultimate Vault Hunter Mode Upgrade Pack in a bundle that's available at a discounted rate over buying each add-on individually.
These add-ons will be automatically downloaded as they are released.
For issues with the Borderlands 2 Season Pass on PC, please contact Steam Support at: https://support.steampowered.com/