Can you count how many apples there are in that parcel?
How many mics do you know of that are adequate for recording?
How old are you, little girl?
This has the same meaning as the kanji, specifically the how many meaning. You know this because you ask "how many" and they answer "つ." This can also be used to ask how old someone is, but generally only for children's ages.
The reading comes from what you learned in the kanji, nice job.