The DP-90se features a function called "AB Repeat", which allows you to choose a specific section of a song, and have it play back repeatedly. This is a great way to practice any trouble spots in a song.
Use the following procedure to utilize this function:
1) Select the song which contains the section you'd like to play back repeatedly.
2) Press the play/stop button to begin playback of the song
3) At the beginning of the portion that you want to be repeated, press the [AB Repeat] button.
4) At the end of the portion that you want to be repeated, press the [AB Repeat] button once again.