alex90, a listening squawk, something I've only just heard of today.
"Listening Squawk" is pretty straight forward, you tune in the frequency, make sure it is correctly set / listen on frequency to make sure you have the correct frequency, set the squawk to the predefined squawk. The controller knows you're listening, and can contact you if they wish, and you know that you can contact them if you wish too.
It essentially saves radio air-time, and a little effort, but in the case of an emergency, they may wish to know which type of aeroplane, how many people on board etc... which you would normally provide when asking for whichever service.
Something to note is that not all ATSU have listening squawks (I believe), and it may be best to look for the particular ATSU's guide / notes...etc...
Perhaps not condescending, but it does feel a bit like if I don't know, I shouldn't be flying, which isn't the right attitude, IMHO.
I don't think that this was the intention of anyone on here. I hope that I say this from all of us: you should never feel that way. A PPL is a licence to learn, not a confirmation of perfection! We ALL have had shortcomings in our training, whether with our flying skills instruction, or with our theoretical instruction. The importance is to realise these shortcomings, and rectifying them before featuring in an AAIB, which you are doing! I can do nothing but commend you for this, and I hope that others do too.
If you feel like experiencing a little busier airspace, PM me, and I'll be happy to show you what it is like out there - maybe get a zone crossing or two! (I fly out of Biggin Hill)