Those are good links but maybe a bit much for a student trying to do something in his room. Here is the simplified version.
Find a builders supply place that sells unfaced semi-rigid fiberglass or mineral wool boards in the 3 to 4 pounds per cubic foot density. Typical makers are Owens-Corning 703, Johns-Manville SpinGlass, and Roxul. Do not use the fluffy batts and you will most likely have to go to a real contractors supply place and not a home improvement store. Also expect to have to buy a full box (24 total inches of thickness of 2 foor by 4 foot panels). Then go to a fabric store and buy some loose fabric (Craft Felt and Burlap are popular choices). Neatly wrap the insulation panels (I use hot melt glue) in the fabric and hang on the wall with a spacer between the panel and the wall. The thickness of the insulation will determine the absorbency. 1 inch thickness will make a mostly high spectrum absorber. 2 inches of thickness will take care of the highs and mids, and for a full spectrum absorber you need at least 4, preferably 6, inches of insulation. Note that the thick absorber absorbs everything, not just the bass, so don't think that you need equal numbers of each type of absorber. Position your bass absorbers in the corners (where bass accumulates) and then put further absorbers on the middle of any parallel walls to cut down on slap echoes.
