Most savory recipes begin with a chopped onion, minced herbs or garlic. You have to either mince, fine chop or dice, medium chop or large chop your vegetables. Occasionally they will call for chunks. This is usually reserved for when the vegetables need to be in quite large pieces, such as for stock. So when you come across chunk or rough chop in a recipe, you can feel confident simply chopping up your veggies, keeping the pieces about the same size and quite large.
The size of the vegetable in a recipe is very important. Primarily it influences how long they take to cook, the overall texture in the final dish and also taste of the dish. A larger piece of celery is going to cook more slowly than a smaller piece. It’s going to taste different. It will also have a different texture and mouthfeel. If the vegetable has a sharp and strong taste, like garlic or chilli, go for smaller pieces, especially if the vegetable isn’t going to be cooked. Raw onions should be sliced thinly or minced finely. Cooked onions are sweeter so they can stand being larger.
With experience you will begin to get a feel for how big or small to make your chop. Until then, picture the finished dish in your head when prepparing vegetables. Consider if you want the pieces to be big and chewy, or smaller pieces will fit better. Think about if you would like to bite into a large piece of your vegetable or if it would be better if it were smaller and less obvious. No need to cut matchsticks or them brunoise. Just keep chopping those veggies.