you'll need an interface if you want to record anything with an analog signal (XLR microphones, electric guitars, electric violins, analog synths etc.) . The interface can also connect your studio speakers through its outputs ...rather than plugging your speakers into the computer's headphone output.
If you just want to make beats, you can make them with your computer using a DAW and midi controllers. Midi runs straight into your computer. Older analog instruments have to go through the audio interface to convert the signal into digital for your computer.
it's a good piece of gear, but get one if you're really serious about producing. They'e easily $100+.