In addition to slowing your music, Capo also allows you to apply effects that will help you during the learning process.
The Mono effect allows you to re-mix a stereo recording down to mono, and adjust the balance while doing so.
This effect is useful for play-along learning material which places a backing band in the left channel, and a solo instrument in the right channel. By enabling the mono effect and panning the slider to the right, you can slow down the solo instrument to help you learn the solo part. By panning to the left, you can hear just the backing band and play along yourself.
Mono also comes in handy for certain popular recordings. There are times when the rhythm guitar part would be mixed to one of the channels, while a second guitar part would be mixed in the other channel. Panning to either side would help you isolate the part you're interested in learning.
Capo includes a 10-band graphic equalizer that lets you increase or decrease levels in specific frequency bands. By adjusting the equalizer, you can make ranges of the audio frequency louder or quieter, so you can more clearly hear the parts you are interested in learning.
For instance, if you are trying to learn the bass part of a song, you can lower the sliders in the high frequency range (closer to the right) which'll result in the bass notes being heard clearly. You can even take it a step further, and raise some of the bass sliders to make the parts even louder.
Capo includes some presets to help quickly set common equalizer settings. When you adjust the sliders from the preset values, they will be saved along with the song, so you don't have to worry about losing your settings.
Capo includes a fairly sophisticated vocal reduction effect that'll apply traditional voice cancelation (out-of-phase mixing) in a specified frequency range. By limiting to a specified range, Capo's voice reduction effect will leave much more of the original song unaffected, so you can create decent quality backing tracks to sing along with.
In some songs, the lead instrument is panned to the center (or very close), so the voice reduction effect will allow you to reduce the volume of the lead instrument so you will be heard much more clearly as you practice with your favorite songs.
In addition to being useful for singers, reducing the volume of the lead singer can help you hear the instrumental parts you're trying to learn.