In the video you'll see the planar elements attempt to breach rifts in Telara, and the players who fight back the assaults. This footage is all taken from the most recent beta event, which you can read our impressions of here.
The video itself is a bit hard to follow, due to everything moving at what seems like 3-4x normal speed, but essentially it's giving you a glimpse into some of the gameplay you'll experience on your adventures in Telara. Rift battles can become rather expansive, and sometimes will require multiple groups of players to overcome. Even though the video is a bit hard to follow at times, you can easily see how chaotic and exciting taking part in a rift event can be.