I am going to jump into this conversation if I may Having the same issue... But don't really understand flash.
I had a flash on my Pentax system but didn't really use it a lot but was nice to have for the odd shots. So now I'm with Nikon I want something cheap (as I won't use it loads), hence looking at Youngnuo.
What's the difference between manual and TTL? Is manual difficult to use? I'm liking the look and price of a 560iii and the inbuilt wireless so I only need one transmitter but will I find no TTL an issue with my lack of knowledge? Would this make it difficult to just quickly pick up and shoot? Is there a different model Youngnuo I should be looking at?
Don't worry, i was the same when i first came into the world of flash photography
I'm no expert, but this is my understanding of the two
Basically a manual flash is just that, fully manual, so you have to tell the flash what setting to use, and this relays no information to the camera, so you will need to adjust your settings in-camera to suit, otherwise everything will be overexposed by the flash
TTL (or Through The Lens) is fully automatic, so the camera tells the flash what power to use and adjusts the exposure accordingly, so essentially works just like your on board flash but with more power and much more adjustment
Maunual flashes are idea for OCF (Off Camera Flash), so to add light to a subject from above/side/behind etc, hence why the 560III has built in wireless, TTL flashes are mainly for use on camera
So the 2 paired together make for a great combination, on camera TTL flash with the addition of an OCF manual unit
Hope that helps