The Groove Pool is a bank of rhythms that can be applied to both midi and audio clips (as long that audio clip is warped and is not in Re-Pitch warp mode). The Groove Pool can be accessed by clicking the Groove Pool icon (2 line wave squiggle icon) which is located at the bottom left of Live’s Browser, above the help/info view box.
Once opened, the groove pool does not show any grooves or rhythms to apply. The grooves or rhythm clips can be found by right clicking in the empty groove pool, then selecting Browse Groove Library, which will take you to Packs, Core Library, Swing and Groove. From there you can browse through the various categories and click on the .agr files to preview the type of swing you want to apply. If you double click on a .agr file, it will place that groove into the Groove Pool. Then you can drag the groove that is in the groove pool onto the clip to apply it to that clip. The clip view box (the skinny box just to the right of the help/info view box) will show the current groove applied to that clip. Pressing Commit will create new warp markers on an audio clip and will snap midi notes to the actual place on the grid where the groove occurs.