Buy and install Garage Band or another recording program onto your computer.
Open Garage Band and select "New Project." Choose what type of project you want to record (if you're making beats, select "Piano"; if you're recording vocals, select "Voice"). Hook your microphone's USB cable and your MIDI keyboard USB cable into your computer's USB ports, one at a time. When you plug each one in, a window should pop up saying, "Number of MIDI inputs changed." Click "OK" or "Accept."
Select "Track" and then "Add new Track" to add more tracks. This allows you to layer tracks, one over the other, to make a full array of instrumentations and vocals. Name your tracks by selecting the track and double-clicking it. Arm the track by selecting the red button on the track, and when you're ready to record, press the record button at the bottom of the window. The track will not record if you don't arm it.
Make a new track. Select "Software Instrument." Change the instrument to drums. Choose what type of drums you want to use (techno drums, rock drums, hip-hop, etc.), and use your MIDI keyboard to make the different sounds of the drum kit. Change the timing of the drums by selecting "Enhance Timing" at the bottom of the window, and choose the appropriate note to align with your drums (i.e., 1/8 note, 1/16 note, 1/8 note triplet). This step can be used to create synthesizers, piano, guitar sounds or anything else that's available on your software. Change the instrument to whatever sound you want and repeat this step.
Create a vocal track by adding a new track, then selecting "Real Instrument." Make sure your input source shows the name of your microphone, and if necessary toggle between mono and stereo until you see that your vocals are being recorded.