Selection -> Sample Loop

Set the loop points based on the selection.

Create Loops in the Audio File Editor in Logic Pro — Apple Support

Selection → Sample Loop: The selected area is used to set the loop start and end points.

Create Loops in the Audio File Editor in Logic Pro — Apple Support

The Audio File Editor Loop commands, available from the Edit menu, are ideal for use with Sampler.

You can also use these functions to generate audio files that contain the loop settings in the file header. This allows you to make full use of these files in any app that can read the loop information in the file header.

Slicing Loops — Power Up With These Six Tips | Production Expert

The ability to slice audio loops up into their constituent hits and map them across the keyboard for unfettered rearrangement has been a staple music production technique since 1994, when the release of Propellerhead’s Recycle! application changed the sampling game forever.

  Add Region/Cell to Loop Library…    ⌃⇧O

This command was renamed from “Add Region to Loop Library” to “Add Region/Cell to Loop Library”. Adding cells from the sequencers seems like a very fine way to create your own loops.

Create your own Apple Loops in Logic Pro — Apple Support

You can create Apple Loops from your own audio and software instrument recordings. When you create an Apple Loop from a region, it’s added to the loop library and appears in the Loop Browser, so that you can use it in other projects.

How to perform with Live Loops in Logic Pro X 10.5: a step-by-step guide

Though they’re terrific for transforming studio-based productions, Live Loops are equally powerful when used for live performance. We demonstrate how this effective feature can take tracks from the studio to the stage.
Mark Cousins — MusicTech

Best Logic Pro Launchpad grid controllers for Live Loops — 9to5Mac

It’s time to take full control of Apple’s latest production technologies with Novation’s Live Loops and Logic Pro Launchpad grid controllers. The Live Loops grid-based environment is a wonderful experience with a connected iPad, allowing for a more immersive approach to your cells via the Logic Remote app. But Live Loops also brings with it official support for a wide range of those colorful and affordable grid controllers from Novation. For compatible models, functionality details, and more, hit the jump.