Explanation, Please

Most of what I know about cars is from what happens when I need service. My '09 vehicle is plugging along with 128,000 miles but yesterday the AC was only putting out warm air. Turns out there was a leak, thoroughly explained and shown to me by the mechanic, which is a simple thing to fix. The big thing is the compressor, and it's okay. The mechanic might as well have been talking about dark matter in the universe or quantum mechanics, but even so, I like to have things explained to me even though I may not understand much.