There are 14-16 vowel sounds in American English. Vowels are made by moving the tongue up and down and front to back. Imagine that the chart below represents your mouth:

In order to understand how vowels are made, let’s practice moving our tongue up and down and back and forth:

Front and Back Vowels: Practice saying the vowels in the words he and who. Can you feel your tongue moving front to back?
iiiy-uuuw-iiiy-uuuw

You can also try alternating between the vowels in day and go:
eeey-ooow-eeey-ooow

And between the vowels in hat and hot:
æææ-ɑɑɑ-æææ-ɑɑɑ

High and Low Vowels: The vowel in heat is a high vowel whereas the vowel in hat is low. Do you feel your tongue and jaw moving up and down?
iiiy-æææ-iiiy-æææe

Now try alternating between the vowels in pool and pot:
uuuw-ɑɑɑ-uuuw-ɑɑɑ