The concept is based on the idea that all learning is relational. Meaning, the more a new subject relates to an already understood subject, the easier it is to assimilate; for use - to learn.
So, if you wanted to learn Latin, start with all the overlap you can find. Alphabet is almost the same, list all the words you already know that are Latin, define the ones you have heard but didn't really know the meaning (e.g. for example), if you know some Italian - look at the crossover, if you are Churchy - think about Sunday mass. The idea is to get a core comfort with the relationships between the new subject and the old subjects. The more the better / faster / deeper.
Also keep in mind the subjects don't need to be as similar as two languages. Sometimes it is easier to pick something very different. Like learning how to read an EKG tape and music - a few percussion instruments timed and played differently based on the condition of the heart. Over time you learn to "hear" the heart beat you see on the paper and increase the sensory experience from just visual to aural - which a heart beat is anyway.
Another example I used as a kid was for trouble-shooting. I studied battles and wars and understood the idea of divide and conquer. This is more of a metaphoric relationship. When I would ask, "which side of X is this problem?" I would know pretty quickly what my choices are - cable, OS, monitor...etc. From there you can visualize problems in ways that are often really helpful. If I could find the right point to ask the question, I could get VERY close to the point of failure VERY quickly. Taking as much ground as possible.
Drawbacks - Finding the right parallel subject matter can be tricky (and fun). Even the act of trying to find associations can be really helpful since you are characterizing the subject matter you want to ingest. That alone creates handles where there were none. Another possible drawback is the personal nature of these associations. They don't always work for everyone. My examples might have sounded pretty useless to you - but that's okay - they work like gangbusters for me!
For general advice on learning I'd throw out my autoruns:
Chunking information into 25 minute learning periods Chunking your time to 25 minutes on, 5 minutes off Build off of what you know Preview your subject Immerse yourself in the subject - all senses Regularity - daily, with reviews Teach someone as you learn - this is my personal secret sauce Neatly write down with pencil in cursive what you need to know Watch Learning How to Learn on Coursera - her voice alone is worth it Keep notebooks for each subject - one subject 5" x 8" Oxfords are nice Keep an index card in your text books for notes, quotes and page numbers
If you add some specifics of subject matter, I bet the crew will have gobs more to offer.