Yes, welcome to the wonderful world of Yugoslav Postal Stationery.
What I am about to say is meant to encourage you, not put you off - so if you find it a bit dry read it in small chunks!
First of all there once lived two holy men called Mr Higgins and Mr Gage. Their mission in life was to catalogue all the Postal Stationery in the world. The Yugoslavia section ends with the issues of 1966. It's helpful to have a copy. The whole catalogue is out of print and costs so much to buy that it would be 20 years before you could afford any of the stamps! But you can often pick up reprints/copies of individual countries cheaply.
They introduced a list of catagories. There is of course no need for you to follow their catagories but it may well help you to understand what other collectors/dealers are talking about if you do.
These are all the catagories that affect Yugoslavia - they didn't issue any of the others:
Postal Cards. This also includes reply cards which are double cards. The receiver read your message written on one half, tore off the other half, wrote a reply and sent it back free, because you had already paid the postage on both halves.
As far as Yugoslavia is concerned postal cards are the most fun. When they had hyperinflation in the late 80s/early 90s they were churning them out to try and keep up with postal rates, so there's a lot to find, often with extra stamps already stuck on to take account of new price hikes.
You can build up a good collection of postal cards quite cheaply PROVIDED that you start in 1921. Before that they were using up old Hungarian cards by overprinting them, and these are complicated and considerably more expensive.
Now, you'd better sit down for this bit. Just before and just after WW2 they issued view cards as postal stationery, i.e. with the stamp already imprinted. Just about every major town in Yugoslavia wanted themselves included -with the result that there are a lot of different ones to collect. Well, to be honest, well over 800 diferent. And most of then cost around £5 sterling. So you may want to limit your collecting of those either to a specific town, or a sample of each different type.
A - Letter Cards. A sheet with sticky edges, which you write on, lick and seal
B - Envelopes
D - Official Cards. For use by the Post Office. There's only one type, though a lot of sub-types. Ignore it.
F(B) - Airmail envelopes
F(G) - Airmail Letter Sheets
H - Telegram Receipt Card. Only one type and I've never seen it. Ignore.
I - Military Cards. Interesting but expensive.
Of course you can also collect postal stationery of pre WW1 Bosnia, Montenegro and Serbia, WW2 Croatia and Serbia,(these are all separate sections of Higgins and Gage) and all the post 1991 states.
Very best of luck
