The cooking time of pasta depends on the variety of pasta you have. It is different for spagetti, penne, tagliatelle etc.
Al dente pasta is firm when bitten without being hard. Proper al dente pasta have a little resistance when you bite into it. Many people like pasta to be less al dente, but some people like pasta to be more al dente.
In Italy, when pasta is cooked until soft, it is called "stracotto", what means it is overcooked.
The general advice how to cook pasta al dente is to cook it 1-2 minutes less than is the recommended cooking time written on the packaging.