When you first start Capo, you will be greeted by an invitation to drop a song on the application. You can drag songs onto this window from Finder, or directly from iTunes.
Once your song is loaded, you will be presented with the main Capo interface:
On the left side of the window you'll find the song's cover art, information about the song, and the Capo heads-up display (HUD). The HUD contains the current position in the song, and controls to adjust playback speed and pitch.
On the bottom of the window, you'll find the volume slider, playback controls, and the zoom slider. In addition, there are also buttons for adding chord entries, toggling the loop, toggling the metronome, disclosing/hiding the song settings, and sharing your Capo documents.
The timeline indicates the current bar/beat position in the song. Clicking in the timeline will allow you to modify the playback position, and holding the mouse button down allows you to "scrub" the audio.
The waveform gives you a familiar waveform representation of the audio data in the song. This is also where you will create and adjust your regions.
The spectrogram display provides a detailed view of the frequencies in a song, arranged in a grid according to the 12 tone music scale. Most importantly, the spectrogram area is where you will enter the notes that you hear so they will be tabbed out below.
The notation area, directly below the spectrogram, is where you'll find the chord entries that Capo detects for you, and the note entries that correspond to the where you place notes in the spectrogram area.
Finally, you'll find the song settings to the right of the spectrogram. Here, you can control the effects, beat settings, and note entry settings. This pane can be revealed by clicking on the button that looks like a set of sliders, to the right of the playback buttons.