Open the Editor, tap the measure where the text belongs, then tap T (iOS) or ABC (Android) to switch the keyboard into text mode.

 

Tap the three lines beside the text box for the texts the player understands, such as D.C. al Coda, D.S. al Coda, and repeat counts like 3x. The up and down arrows move text vertically. Press Return, or type two slashes (//), to start a second line. Tap the check mark (Done on Android) to leave text mode.

 

Some users write lyrics with the text tool. See the Lyrics thread on the Forums.

 

For the full guide, see Edit a song on the iReal Pro website.