Pad folds (prefolds and terries)
The simplest thing you can do with a flat nappy is pad fold it. Just as the name suggests, all you do is fold the nappy into a pad and then place it in a wrap. Because it's the wrap holding the nappy in place, you need to use a close-fitting wrap with a gusset so that the pad doesn't slip around inside the wrap.
There are diagrams and instructions on folding prefolds on the Nappy Lady website.
In pocket nappies (prefolds and terries)
Flat nappies are ideal for use in pocket nappies. These are wraps which have two layers, making a pocket. You stuff the pocket with the nappy (folded into a pad) and you have an all-in-one nappy. If you stuff the nappy in advance, it will be easy to use, even for an inexperienced cloth-nappy user. Most pocket nappies have a waterproof outer layer, and a soft inner layer. The absorbent flat nappy is placed between them. Before you wash, remember to pull out the flat nappy.
Examples of pocket nappies include:
(N.B. there is at least one type of pocket nappy which does not have a waterproof layer, and which must be used with a wrap. In this case the stuffing you put in alters the absorbency and bulk of the pocket nappy, which is then used as a shaped nappy inside a wrap. An example of this sort of pocket nappy is the Stuffie.)
Nappy fasteners
Nappi Nippas or Snappi Fasteners are an alternative to pins and are designed for use with terries. Here are instructions on how to use them.
Folds for Terries
These are folds where you need to fasten the nappy with either a pin or a Nappi Nippa. Terries can be folded in many ways and you can find a few different ways of folding terries on the Nappy Lady website. It includes the traditional kite fold and the very effective, yet simple, bat fold. See also the Sydney Nappy Wash website's page on folding terries.
Pinning prefolds
Prefolds can be pinned or fastened with Nappi Nippas (some prefolds work less well with Nappi Nippas than others, depending on the density of their weave). You can find some folds which work with pins or Nippas on the Nappy Lady website. The US nappy laundry Dy-Dee also has a page with links to a selection of folds. And there is a really, really simple selection of folds on the This Baby of Mine website.