I've had a steam account for a long time but only ever had two games, both bought for me retail as gifts, and never dealt with DLC or season pass before this.

When I installed Fallout 4 I thought I saw something about having a season pass with it, but can't find any information about it looking at my Steam account. Is there a way to check?

If I don't have it, can I purchase it through Steam?

Yes, if you go to the game's store page on Steam, it should be listed under DLC.

http://store.steampowered.com/app/377160/

Look under "Downloadable content for this game"

Thank you. I've got it all sorted out now.

Any time.