Well, al dente means to the tooth... Not helping? What if I say "tender on the outside but firm on the inside, so that you can fully feel the texture of each bite of pasta with your very own teeth"... Oh boy, pretty impressive, isn't it?
OK, but let's get practical. What I learned from Mom (a directly-imported-from-Italy lovely and charming person) is:
1) There is no prespecified time... it all depends on too many factors (not a great help either, but please continue reading)
2) The time you read on the cooking directions of the pasta you bought is always very helpful
3) Try to buy real Italian pasta. The wheat is just different and cooking times are more precise, and...
4) YOU SIMPLY HAVE TO TASTE IT, beginning 1 minute before reaching total time cooking according to the directions you read (following Step 2). It's ready when you think it's reached the texture you and your family like.
So, remember: YOU SIMPLY HAVE TO TASTE IT; and forget burning your fingers trying to throw pasta on the wall.
In bocca al lupo! (Good luck!)