Origami is the art of folding paper into objects, shapes and animals. Origami creations range from the simplest of jumping frogs, to complex paper structures, but it all starts with the same basic folding techniques. Getting these basic folds right is essential, one untidy fold can cause untold problems further down the line, so try to get the edges of your paper lined up exactly unless told otherwise.
Before we start, it's important to know that the dark side of the paper in these diagrams (and all origami diagrams, really) corresponds to the colored side of your origami paper. You can buy origami paper online in a variety of different colors and patterns to suit your project.
The valley fold is the most basic of basic origami folds. Simply fold the edges of the paper upwards and together, making a smooth crease down the dashed line. A valley fold can be vertical, horizontal or diagonal.
A vertical valley fold that results in the paper resembling the shape of a book is called, funnily enough, a "book fold".
The mountain fold is the opposite to a valley fold. Instead of folding the edges of the paper up, fold them down along the dotted line. Easy.
Notice the difference between the mountain fold line in fig.2a (dashes and dots) and the fold line in fig.1a (dashes). While it will usually be obvious either from the next stage of the diagram or from the written instructions whether you need to valley or mountain fold, these lines are pretty universal in origami so you can always be sure which is meant.
The cupboard fold is actually a combination of folds. First create a book fold and unfold again, leaving a vertical crease down the center of the paper.
Now take the left edge of the paper, and valley fold it so the edge lies along that center crease. Repeat with the right side so the paper resembles a pair of cupboard doors.
Outside reverse fold
When you're asked to make an outside reverse fold, you're probably starting with an already folded piece of paper similar to fig.4a.
Valley fold the tip into the position you want your outside reverse fold to end up in. Compare the positions in fig.4b and fig.4d to see what I mean. Unfold, and then do the same thing except with a mountain fold. Unfold again, and you should be back to the position in fig.4a with the addition of creases where the valley fold line is in the diagram.
Now, fold the tip backwards. You'll need to open the tip slightly to get it to fold correctly, as in fig.4c. Once it's in the correct position, flatten it down again and make sure the valley folds to either side are crisp.
Inside reverse fold
As the name suggests, the inside reverse fold is a similar concept to the outside reverse fold, except the tip is folded inside the model instead of outside it.
Valley fold the tip into the position you want your inside reverse fold to end up in. Unfold, and then do the same thing except with a mountain fold. Unfold again, and you should be back to the position in fig.5a with the addition of creases where the valley fold line is in the diagram.
Now, push the tip down, inside the model. The sides will open up slightly, and you should have a crease down the center which you can valley fold easily. Once the valley fold is made, flatten everything down and smooth the mountain folds where the tip disappears inside the model.
These are the basic folds that you'll see over and over again in origami tutorials. Many tutorials will not go over the meaning of these folds so practise until you're confident that you can remember the meaning of each, or of course you could just bookmark this article and come back whenever you need to.
This is the start of a hopefully long-running series on origami techniques and tutorials, so stay tuned for something a bit more advanced.