Basically it has different layers depending on the babies age and what they are eating, there is a paper layer first which works once the poo is more solid more than whilst the baby is being breast fed where it tends to be a little too squidgy although you can still use a paper layer I guess. This is a thin layer like the thin inner layer of a disposable.
Then there is what they call a booster, which is for if you are likely to leave the baby in the nappy for longer, like if you are out and about or at night times. This is made from Bamboo, cotton or a microfibre, depending on the style you want to go for.
The next layer is pretty much like a fitted and velcrod terrys nappy, it basically looks the same as a disposable but made of again Bamboo, Cotton or a microfibre. This is sort of similar to the middle cotton wool type stuff that's in a disposable nappy.
Finally you have what they call a wrap, this is a bit like the plastic outer layer of normal nappies.
When the baby needs changing, you would throw away the paper bit, Wash the booster and the actual nappy and re use the wrap (Usually lasts a fair few changes before it needs cleaning as it's waterproof and obviously therefore wipeable!)The different materials that I mentioned are all slightly different with their own sets of pro's and cons. Bamboo, really absorbant, excellent material but takes a long time to dry. Cotton, Medium absorbancy, fab material, usually slightly cheaper, medium drying time and then microfibre, not so great absorbancy (Still probably better than disposables) But dries pretty much as soon as it's out of the washing machine.
You can actually buy tester kits and things from the websites. if you wanted to buy one to look at. A kit of 10 reusables with boosters, 3 wraps, a pack of paper liners (Think it's 200) plus a bin to store wet nappies in is around £115 at the moment from littlelambs or "greenabubs"
Hope this helps a little bit! I used my sisters website of "clothnappytree" which has really helped me to get my head around it all!
Hmmm..... not sure if I've just rambled on for ages now sorry all!
xxx