There are essentially 4 basic types of knife cuts that you will find in most recipes. Uniform cuts are good for presentation, but they also ensure all of the food will cook evenly.
When you see steak fries or chips, they are typically going to be cut into a baton that is about 8 mm thick. If your recipe calls for medium dice, it is simply a baton cut into 2 mm cubes.
A julienne cut is often called the matchstick cut. As the name suggests, you will want a very thin, stick-like cut. In order to make this cut, you will want to square off the vegetable and then cut into 3mm thin rectangular slices. Cut these slices into the thin matchstick.
This is the cut that is used most often. It is simply a rough informal cut. You simply cut the vegetable into thin slices without squaring it off.
For cutting up leafy vegetables and herbs, you will use a chiffonade. To perform this cut you will simply roll the leaves together and then cut perpendicular to the roll. This will leave ribbons of herbs for garnishing or for a saute.