Eden prime is a colony that was a peaceful and flourishing colony on the edge of Citadel Space. It was the first colony created by humanity and as such is viewed as a beacon of hope for humans in an ever threatening horizon. It is also here that the first mission takes place in Mass Effect 1.
In the events of Mass Effect 1, the colony is raided by Saren Arterius, upon hearing of the discovery of a Prothean ruin with a beacon of some form, Saren cleared out any humans in the vicinity and interacted with the beacon, gaining allot of valuable knowledge of what happened to the protheans, the reapers and their culture.
After using the beacon as he intended, he ordered heretical geth which followed him believing he was a god, to order heavy explosives to be placed on the cargo bay which would from the explosion, destroy the entire colony.
Defusing the bombs as the plot goes, Shepard will encounter moderate resistance from Geth and Husks freshly released from the Dragon's Teeth impalement structures. After a brief moment of fighting after clearing the bombs, the player will encounter the beacon used by Saren, stepping near it causes Ashley to be drawn to it physically but Shepard intervenes the second Kaiden tells her not to touch it. As Shepard pulls Ashley away from the beacon, he is drawn to it unintentionally and for a moment appears to be in extreme pain or severe muscular contraction before floating and going bolt upright, experiencing an imbedding process full of images of prothean knowledge of what happened before they went extinct.
The Beacon was a device which the Protheans used to relay information to each other with the beacon as the source of the relayed information, where it appears that it would transmit information neurologically directly to the brain.
Saren viewed his effort on Eden Prime as a major victory, unaware until a point after, that Shepard had prevented the destruction of the entire colony and had actually made use of the beacon.