Have you recorded a software instrument that turned out a bit too sloppy timing wise? Try quantizing. When you quantize notes, they will end up on the beat instead of in between beats. In short, you are aligning the notes to be exactly on-time.
You can choose to quantize your recording either in the region Edit menu or in the Piano roll. The Piano roll allows you to see what happens when you quantize, so let's start there:
Choose a track then click Piano Roll
1. The Piano roll will pop up and show all the midi notes.
2. Select the notes you want to quantize, either by clicking and dragging a selection, or click once anywhere in the Piano roll, and press Cmd/Ctrl+A if you want to select all of them
3. Right-click and select Quantize and choose your desired subdivision
4. If you're unsure which subdivision to choose, 1/8 or 1/16 will work in most cases.
(1) Open the MIDI track then choose Piano Roll
(2) Selected notes in the Piano roll. Click and drag to highlight notes
(3) Right-click any note the Piano roll to access the menu. Select Quantize and choose a subdivision.
Note: You can also access the Quantize option by hovering your mouse on a region, click Edit > choose Quantize
If you want to quantize all notes in a region, there is an even quicker way of doing it without opening the Piano roll:
1. Hover over the region and click Edit
2. From the menu that appears, select quantize and choose a subdivision
3. You're all set.