The accompaniment style decides what the piano, bass and drums play behind your chords. Tap or click the style name in the player controls and choose from the 50 styles built in, grouped as Jazz (27), Latin (8) and Pop (15).
 
Three more groups are available as an in-app purchase: Blues (12 styles), Brazilian (11) and Salsa (17).
 
On Mac and Windows the player controls sit on the right, or along the bottom when minimized. Choosing a style can change the tempo, since each style carries a default tempo of its own.
 
For the full guide, see Accompaniment styles on the iReal Pro website.