Hi, Optimus. Not sure why this is giving you a hard time but it should be rather easy. I just went and tried it out to make sure I remembered how to do it.
I'm going to assume you have recorded your clip to a metronome so it matches up to the timeline and that you have used your Snap settings to trim the clip to fall within a measure, beat or whatever musical time based period you want the loop to be AND that you have "Split at zero crossings" set in Preferences OR you have made sure the beginning/end of the clip have been faded appropriately to avoid pops when looped.
1) Select the clip you want to loop.
2) Right click the clip and select "Groove Clip Looping" from the context menu OR simply press Ctrl + L
Your clip is now a Groove Clip. If you drag it out it should repeat and the start of the next instance should appear at an exact Beat, Measure, whatever on the Timeline.
Now here is the part that might be causing you problems. If you want the Groove Clip to follow any time changes you have to...
3) With your clip (and only that clip) selected Press "I" to open the Inspector
4) Click the "Clips" tab at the top of the Inspector window
5) Click where it says "Groove Clip"
This will show you the Groove Clip options for the selected clip. You can see various information and options for the clip.
6) Checkmark the option that says "Stretch to Tempo"
Now if you change the project tempo the clip will adjust to follow the new tempo.
You can do this with any audio clip. You can export it to a special folder on your hard drive (that you create) and then just drag it into any project you want. I am not sure if the Groove Clip info will follow it (in which case it should simply follow the current project tempo) but you can always drag it into a project as is and use the Timing Tool to make it fit in time where you want.
You will need to render any time stretched audio though to avoid artifacts (what you will hear is Online rendering... what you want is to Bounce to Clips so you are using Offline rendering which produces much better results). Also advance Audiosnap features can let you do some really crazy stuff as does Loop Construction but simple looping is... well pretty simple.
Cheers.