If you want to quantize your audio manually, you can use the timeline ruler within the track editor window to divide the audio waves into beats and place drag markers on the notes.
Track Editor Window
Change the Note Type View
Add a Drag Marker
Zoom In
Track Editor WindowWhen you select a track, the track editor window produces its own timeline that you can use to edit he audio region. The two timelines can sync together.
Change the Note Type ViewYou can change the note type view by clicking on the top right corner of the timeline box. Scroll through the note options and select one to divide the audio region into beats. Your playmarker will snap between these beats on the timeline.
Add a Drag MarkerIf you want to place a drag marker on a note that's in between beats, you can select a smaller note type and click on the beat.
Zoom InYou can further edit the audio by zooming in on the waves in the track editor window.