Loopers Loopers, I do love Loopers.

It's best to put them after effects to preserve what you're playing in the loop.

And if your amp is so equipped, put it in the effects loop send to get: 1.  The full flavor of your sound coming out of the amp front end (gain/drive) and, 2. To keep the recorded loop in playback mode from going back through the amp gain a second time.  This really matters when you change gain or other effects on the amp going from Rhythm 1, Rhythm 2 if you have that, and Solo.  Keeps the voices separate.

And this will let you experiment with two, three or even four layers of loop.  Keep in mind the more layers, the less busy and more space and varied voicing you'll want for each layer.  This really makes you think about arranging (and playing with others- not stepping on each other's sonic footprint).