Folding paper is a very versatile technique, and you will
never know everything about it or be able to explore all
its possibilities. The secret is to find out what it is
about folding paper that most fascinates you ... and to
concentrate on that.
If you would like a broad, but quite detailed, overview of the many types of origami that are out there, some of which are truly wierd, you can have a look at the page on this site called A Family Tree of Origami Design Styles. Links on this page will lead you deeper into the maze of understanding if you are happy to go there.
Alternatively, you may already know that what really interests you about origami is folding paper into interesting and attractive designs like animals, birds, flowers and ornaments. In this case you will probably be more interested in learning more about the distinction, which you will find everywhere on this site, between single sheet designs, multiple sheet designs and modular designs.
Single sheet designs are just that, designs folded from single sheets of paper, most usually from a single square. Most traditional designs are of this kind. The challenge of folding from a single sheet is in finding sufficient bits of the paper, in the right places, to create what you want to end up with. A horse, for instance, has four legs, a tail and a head. But a square only has four corners. How do you find, and free up, the bits you need for the rest? Because of this, many single sheet designs tend to be challenging to fold - though there are many simple single sheet folds as well, of course. But you may feel that challenge is a very good thing ...
Multiple sheet designs are also just that, designs made up of several, or many, sheets of paper which are then placed or joined together to create the finished design. The advantage of this is that each of the pieces can be folded in a much simpler way. There is less challenge in folding multiple sheet designs but the end results are often much cleaner than their single sheet equivalents.
Modular origami is a special instance of multiple sheet origami where several sheets of paper are folded into simple geometrical paperfolds, called units or modules, which then fit together to create an attractive, and sometimes quite complex, design. Modular design is one of my specialities and you can find a lot more technical detail about it here if you are interested.
Whether you are most interested in single sheet, multiple sheet or modular origami will probably depend on the kind of mind you have. There are diagrams for many of my own designs in each style on this site, which should make it easy for you to try them all out. However, I don't do complex or difficult. For that you must look elsewhere on the web.
One more basic difference between types of origami that is worth knowing about is whether the paper is folded dry or damp. Most paper is capable of taking a sharp crease when dry, but whether you want to crease sharply, or fold loosely, will depend on the purpose of the fold within the design. Damp paper will not take a crease but, like cloth, it can be easily moulded into rounded shapes. Unlike cloth it will hold those shapes when it dries. For some strange reason folding paper while it is slightly damp is called wetfolding (though if you try folding paper while it is wet you will find it doesn't work too well). I generally prefer to fold paper dry and to use sharp creases, but that is a matter of individual taste.