Set the metronome if you want to (it even has a Tap Tempo feature), hit Record, and you’re rolling. You can even overdub as much as you want, layering over your original part, and you can easily export your recordings as audio via File Sharing, email or Copy.
Here’s another cool feature. When you’re in the Record window, pressing the little keyboard icon gives you an alternate keyboard view, which shows you the full keyboard. When a recording plays back, the sounding notes are highlighted in real-time, which can be a great way to see how something was played.