Ok, let me clarify a few things since I love this technology so much, even though I am a techno n00b. (don’t even own a computer, lol)
Do not buy the single pedal looper. You have to upgrade to the new version of the Jam Man in order to get what you need. MF sells it for $299, so only $100 more than the single pedal one. (The single pedal one looks like a “real drag” to use since you have to double click the switch to stop it, you cannot cancel out vocals from recordings, and there may not even be the auto-start-at-the-first-hint-of-a-signal capability, which is a must, for example.) The new Jam Man has little metallic button-pedals compared to the old Jam Man, btw.
As to what I’m doing when I’m trying to learn something, let’s continue with the Half Step routine I set up last Saturday. I’m doing everything from a CD in my CD player and the CD player can pause at any point in time within the song. Not only that, but it can rewind back to any point in time to try to hone in on where to start a loop snippet. Computers can do this too. (I suppose a lot of stuff can do this.)
When I first tried Half Step, I only had about 10 slots in succession to fit into the looper for learning the parts of the song I needed to work on. (like the Jer leads) So I compromised my learning the leads to two snippets for each entire lead. These snippets were WAY too long and I couldn’t work up a breakthrough into exactly what Jer was doing. I’d learn the first few notes, hit the stop, then repeat, but then when I’d try to get the next few notes, the first few would have to play first and before I knew it things would jumble together in my mind and the process would bog down considerably, without advantage. Slowing things down would mean waiting even longer for the latter notes that I was trying to learn to come by, and things would really bog down. So, I knew I had to subdivide the Jer phrases even further and stop being so lazy about deleting previous worthless files or shifting files to new locations to make enough room (unoccupied files) to get all of the snippets for Half Step lined up in succession.
My CD player has a microphone outlet that matches the AUX input of the Jam Man. That’s the feed. This is the same size output as that from a computer, so you can go to archive dot org or You Tube, for example, and apply the same approach using your computer in the same manner that I do using CDs.
When you’re doing all of this, your guitar is not in hand. To get this all working, snippets lined up in a row as partial phrases, it takes probably an hour or more. But once you’ve got it right, then you’re off to the races on learning a song.
The output from the looper goes into an amp, or maybe you can direct it to your computer’s speakers. Don’t know. I use an amp. When you play the song from the computer you hear it through the amp, not through your computer’s speakers since the patch cord mutes the computer’s speakers.
Here is an example that may help you. On You Tube there is the JGB Reuben & Cherise, the really tasty one. At the end there are the really nice solos. The two-pedal Jam Man has the choice of what the noise cancelling will be. Toggle through it while you listen to the song playing through the Jam Man into your amp and choose the setting that brings out Jer the best.
Stop your computer just before the start of the tasty solo. Set the Jam Man on Auto Start and hit the Record pedal. (It will wait for a signal before turning on and start recording.) Then, using both hands, one hand on the Jam Man Stop pedal and one hand on the computer start/stop playing capability, hit the computer start/stop. The song will start playing and be recorded exactly where you wanted it to. Then just as the last note of the short snippet finishes, maybe a quarter of the Jer phrase, hit the Jam Man Stop pedal and hit the computer start/stop.
Next, review the Jam Man recording to see if it got it right at the start and stopped where you intended it to. If you like it, then save it. If not, then start over. Let’s say you liked it and saved it. Now move to the next higher number file location. Your computer will already be at the right point in time for the next snippet. Repeat the process again. And so on, and so on. Try to make the snippets perfect phrases. This means that if you could see the music as sheet music, your snippets would start and finish at the beginning and end of a measure.
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Also, i heard somewhere a while back that keller williams used a jam man for a while. is got two pedals must be better. 
