Cherish, yes you are understanding it

prefolds are a double layer of fabric, with some extra layers in the middle panel
trifolds are a double layer of fabric

both of them, you fold into three

so the TWO layered item, becomes six layers (for trifold) and a few more (say 8) for the prefold

i found six layers of bamboo fine for a nb bub AS the nappy itself.

many companies call a trifold a different name, to make a "point of difference" for their product, but basically, a double layer of fabric, around 30 x 30cm, is a nb trifold/defacto prefold.

many names for what is essentially the same thing.

if you can fold an A4 bit of paper into three, you have just passed the test for folding a prefold/trifold! it's that easy.

looks like a pad once you've folded it
you stick that into a nb sized cover, lay a microfleece liner on top of the "pad" and then put baby in it

if you have a snug fit (e.g a nb sized cover on a nb) you won't need a snappi
if you have a loose fitting cover, then you will need to close shut the prefold/trifold with a snappi.

dead simple, which is pretty essential, when you have a nb and sleep deprivation going on!

i had a very frequently, runny, explosive pooper, (we're talking 20 changes per day here!) so i found covers with leg gussets to be Da Bomb (in terms of pootainment value). Good fit is everything. if you got gapes (tummy or legs) then you will have leakage.

And i learnt in the first week, DO NOT PUT COVER ON LOOSELY! Do not buy a "too big cover" thinking you will save money. i was WEARING poop allover me (changing my clothes and clearning the furniture endlessly) until i learnt this valuable lesson from very patient mcn mums online. My baby is NOT made of china and i need to do up the covers firmly - this was hard lesson for me, i was so scared of doing up the nappies too tight! oh well, it was all new to me. Plus i had been too scrooge to buy nb covers - so of course they were too big. Once i bought nb sized covers, did them up firmly enough - NO MORE LEAKS! yeh!

i had to learn the hard way (i had thought nb sized stuff was a waste of money up til then). and i had a 3.79kg bub - which is not small i was told. but we STILL needed the nb sized covers and nb sized trifolds. All was not lost, was easy to onsell the nb sized covers afterwards, and we kept using the bamboo foldups for two years after that. (as boosters in other nappies).

If you have bought OSFA pocket nappies, they will often have microfibre boosters to suit baby at a variety of ages. Is there a nb sized booster also? Nothing to stop you stuffing those pockets with a bamboo trifold INSTEAD or AS WELL. My baby outwet the microfibre boosters pretty early. they're good cos they dry fast, but you'll notice, the things that take longer to dry, also absorb more fluid.

Some of this is personal preference too.
you'll find different makers use different sorts of bamboo.
you might get one trifold made ALL our of bmaboo fleece (e.g baby beehinds foldups, pea pods bamboo inserts - another excellent trifold)
you might get one trifold made from ONE layer of bamboo fleece and ONE layer of bamboo terry
they will vary in sizing too
buy a microfibre car cleaning cloth at big w and you have yourself a microfibre trifold. microfibre fabric doesn't have as much OOMPH to it, so will not hold the shape well, i found these harder to physically put in a pocket, but it is an option. We tried it, but it didn't last very long for my bub, the bamboo and hemp trifolds were much more suitable (for my child).

Sherpa is another thirsty fabric, i don't see much made out of it anymore, but it's good stuff. And i had a soy/bamboo fitted nappy, that had a trifold snapped inside it, that fabric was very thirsty. i saw soy Cute Tooshies (OSFM fitted nappy that does up with side snaps) on sale at nurture nappies recently. We only had one but gee it performed well. (by the time i found those, we had enough nappies, coudln't justify getting any more, wish i had found them earlier).