This is your first playable mission as commander shepard. This level is not that long and will be rather easy to complete.
You will start off with Kaidan Alenko and Jenkins as your allies. Walk foward a bit and you will notice floating gass bags, or at least that what I call them. Turn to your left and you will see a passage. After walking down this passage for about 6-10 seconds a cut scene will appear with Jenkins taking point and a few geth attack drones killing him. Continue forward and you will get another cut scene. You will meet Ashley Williams for the 1st time. Ask her to join your squad after the cut scene is finished. Progress to the dig site. You will see another cut scene with some talking between Nihlus and Saren. After the cut scene make your way down the path and you will be confronted by geth troopers and Husks. Kill them all and make your way to the cargo train control panel. You will have to fight off some geth troopers on the way to the panel. Once you are there activate it to get to the next area. Your almost done. Just a few more minutes. Once you reach the end of the line on the cargo train you will disembark and you will now need to disarm 4 bombs. Use your mini map to locate them. They are marked as white flags on your mini map. They are not to hard to find. Once you disarm all 4 bombs make your way to the beacon. Of course there are geth troopers waiting for you there. In addition to the troopers you will need to kill a few husks. this should not be a problem. Once they are all dead make your way to the beacon. Achievement unlocked!