Unless your speakers are powered, you’ll need some sort of amplifier to drive them. A great choice for a dorm room is one of the new compact amplifiers with Bluetooth built in, such as Dayton Audio’s DTA-120BT. Even though it’s just 2 by 3½ by 7½ inches, the DTA-120BT puts out 40 watts per channel into 8-ohm speakers, plenty of power for a small space. You can use its built-in Bluetooth to hook up wirelessly to your phone, tablet, or computer, or connect to its line input with a wire.
If you want something more capable, check out NAD’s D 3020 V2. At 30 watts per channel, it’s a little less powerful than the DTA-120BT, but it adds a phono input for connecting a turntable, and digital inputs for connecting a TV or an audio streamer such as Google’s Chromecast Audio.