MusicTechHelpGuy breaks down Logic Pro's pointer tool and the grid system it depends on. The pointer tool moves, trims, and loops regions, but every action snaps to whatever grid is active in the background.
That grid is defined by bars, beats, divisions, and ticks. Checking the LCD display in custom mode shows your tempo, time signature, and current grid division, so you always know what resolution you're editing at.
Switching the grid division changes how fine your edits are: 16th notes give four divisions per beat, 8th notes give two, and triplet settings (8th or 16th note triplets) split beats into three or six for swung or compound rhythms.
If you're new to rhythmic counting, stick with a 16th note grid. It covers the vast majority of editing situations without forcing you to think about music theory.