Chopping is the technique of cutting ingredients into small pieces of an even size. The cubes do not have to be perfectly equal, but should approximate the same size which ensures that they cook evenly. Chopping can be done roughly or finely: roughly means pieces of food about ½ inches, whereas finely means much smaller pieces.
You should always use a knife that you are comfortable with. Practice on soft foods like cheese, melon or bread and get a feel for how the knife works before you try chopping harder foods like onions or potatoes.
The midsection of the knife is used for most chopping tasks, such as cutting tomatoes or apples into wedges, and carrots into rounds. Use the heel (closest to the knife handle) to chop herbs, remembering to keep the fingers of your guiding hand slightly curled under to prevent cutting them.
To ensure the vegetables don't wobble around on the board while cutting, first cut them to form a flat-bottomed base. For instance, when cutting an onion, cut it lengthwise in half then lay it cut-side down. When cutting a potato or carrot, cut off a thin slice from one side then lay the flat cut-side down to finish cubing the vegetables.
When chopping an onion, first use the tip of the knife to cut evenly spaced slices into the onion, leaving the onion attached at the root end. Then turn the onion 90 degrees, and use the midsection of the knife to cut crosswise through the slices to form small cubes.
Lastly, always use a sharpened knife. Dull knives will not only make chopping more difficult, but can easily slip and cause injuries. If your cutting board tends to slide while you are chopping, place a damp towel underneath the board to keep it in place.