Apologies for this sounding like a copout answer, but if you are wanting to record, I would recommend simply doing it in software, since you can monitor (hear) in realtime your looping, and immediately punch in and record it without having to deal with two separate processes and breaking your creative flow.
That said, I would recommend a hardware device only if you need something to be able to loop and practice and won't have your Macbook around, etc.
At the outset, you might consider investing in a simple but high quality A/D interface like: the Apogee JAM (http://www.amazon.com/gp/product/B00H02C9TG/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B00H02C9TG&linkCode=as2&tag=r0a90-20&linkId=VTSVPFKAKKCQMIOX) or Apogee ONE (http://www.amazon.com/gp/product/B004350HHE/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B004350HHE&linkCode=as2&tag=r0a90-20&linkId=Z7N62UUC4T4BELIT)
The JAM is an instrument-level input (it says it's for guitar/bass/etc but will work for any instrument), so if you are recording with a cable, which I assume you might be, working with a looper, then this would be an ideal way to get audio into your computer. Apogee is known for really high-end analog-to-digital converters in the pro audio world and they essentially are giving you a single converter in these products. The JAM also comes with cables to connect to the iPhone and iPad so you can use it with music apps on those devices, and there are looping apps for those, which would lend to practicing (and even recording, though it's virtually impossible to get a truly professional sounding mix coming out of those devices due to the limitations of the software). The ONE device also has an instrument-level input, but has a microphone input (with 48V Phantom Power), so if you are miking your instrument, this would be the way to go. I have used these devices before (they make some others with more channels, but in the same line) and others have been astonished at the level of quality coming out of the A/D conversion for the price. They also integrate perfectly with all Mac audio software and can even be used as your primary audio device for listening to music, etc.
So, on to my recommendation for your situation, software wise:
What I would recommend is Logic Pro X, or possibly Ableton (the Intro edition), since they are affordable. Logic Pro X is a much more capable and full-featured program, and should you decide you want to do more, like bring more instruments and more production elements into your works, it will give you room to expand in that area.
[Full disclosure: I own both programs. I have used Logic for about 20 years and Ableton for about 2 years. I like Ableton, but find that it is geared towards electronic music production. Logic covers both electronic music production as well as studio/audio music production (as a full competitor to Pro Tools), and out of the box has about six times the number of virtual instruments as Ableton, and even more in the way of effects, all of which are universally praised for being studio-grade and not requiring third-party plugins to make a professional sounding song.]
With Logic, or any sequencer, the first thing you want to do is familiarize yourself with how a sequencer works. It is a nonlinear editor program that records your performances. It has a lot of great features for managing your takes, punching in, and seamlessly gluing these takes together for production (Logic is more advanced in this area which is why I recommend it, too).
Logic also has a stellar plugin called Delay Designer. It is capable of designing delays to your heart's content. You can stack and arrange as many of them as you want, as well, and they are non-destructive. So you record your performances, and can choose to hear the effect in realtime, or turn it on afterwards, but either way, your performance stays the same. You can then experiment with changing variables to get exactly the right sound you want.
As for layering, this is where tracks come in. You add another audio track, and record to that track, also using Delay Designer or whatever effect(s) you want. You do this and repeat until you have your song.
There is also the concept in sequencers of setting "loop points", where you choose a region (say sixteen bars) and record over those sixteen bars, on a single track, over and over, and it will capture your performance on that part of the song every time it loops. You will be playing to a tick track that only you hear (in headphones), so you will know when it begins and ends), and can see it on the screen as well.
You then do some mixing–adjusting the levels of each track relative to each other (including panning and effects), as well as EQ and Compression, which are a bit more advanced, but very much worth learning about if you are going to be releasing songs.
Then you "bounce" your track (the term for doing a mixdown–mixing the complete sequence into a stereo file) which can be an MP3 or whatever you would like, and you have your music!
This is a simplified version, and there are many things to learn about this process, but what I've just described is how most musicians would approach what you are wanting to do. You need a sequencer, and you need a good looping/delay plugin.
I hope this helps some.