After the completion of season 1 of Attack on Titan, there were two OVA episodes that were made and bundled with the manga. These two 25 minute episodes expand upon the story a bit. So far, only one has been released.
Part 1 focuses on the 49th Expedition outside the the walls (the one involving Eren is the 57th). As is shown in the episode, what is discovered during 49th Expedition is what pushes the Survey Corp to develop greater means of capturing and studying the Titans.
This episode builds upon the mystery surrounding the Titans, but it does not answer any questions with regards to plot. It does, however, offer hints, but I cannot for the life of me offer any speculation or theories.
This episode also focuses on Hanji Zoe. I personally do not care much for her eccentricity, but I still enjoyed this episode nonetheless because it still remembers to focus on the Titans.
In short, this episode is exactly what one would expect from a normal TV episode.