Instructions found on http://www.foldnfly.com/1.html#Basic-Dart
You will need a sheet of square paper.
1. Fold the paper in half.
2. Unfold and then fold the corners into the center line.
3. Fold the top edges to the center.
4. Fold the plane in half.
5. Fold the wings down to meet the bottom edge of the plane's body.
Here are the video instructions: