Living world releases will be added to a new story journal that can be access via the hero panel.  

Anet: To unlock an episode and have it added to your story Journal, you simply need to log in to the game during the two-week period that the release is live to be given permanent, free access to the storyline of that episode. Once you’ve unlocked it by simply logging in, you can replay that episode’s storyline on any character on your account as many times as you like from your story Journal forever.

Achievements within story steps from episodes will operate very differently as well. Once one character on your account has completed an episode in their story journal, every character on your account will have access to a set of challenging achievements. At any time once unlocked, you can return and attempt to replay that episode in order to complete the achievements. The achievements will be much more difficult to complete than those traditionally found in Season 1, and are intended to be challenging achievements for skilled players to overcome. Each achievement will award both achievement points and material rewards.

More Information:

https://www.guildwars2.com/en/news/introducing-the-story-journal/?utm_source=client