How cooked you eat your pasta is obviously a very personal thing. Different people will cook the same pasta for as much as five minutes difference and each will claim that they have cooked their pasta perfectly. But, while accepting that taste is a subjective thing, there are definitely people who undercook their pasta and people who overcook their pasta. Undercooking is less common because undercooked pasta is crunchy and obviously indigestible. Overcooked pasta is limp and loses its shape easily. If you overcook pasta you might as well throw it away and start again as it will taste disgusting!
The key to cooking pasta well is to keep testing it as you cook it. There will be a guide cooking time on the packet so about a minute before that time is up, start tasting the pasta. It will be ready when it is slightly firm to the bite – a state the Italians call al dente – but with no crunchiness. At this point you should turn off the heat and drain the pasta in a colander. Shake the pasta to get rid of all the excess water (you need to be especially careful to do this properly if they are pasta shapes which might catch pockets of hot water) and serve immediately. The pasta continues to cook while you are draining it in the colander, so when you are tasting remember that what you eat will be cooked for approximately a minute longer during the time when you are draining and serving it.