I suggest you find some lists of minimal pairs on these vowels. Here is a way to think about it: hat - aaaaaaa sound, like when the doctor is checking your tongue hot - awwwww sound, like when you see a cute baby hut - uhhhh sound, like when you don't know the answer to a question.

Here you go, Irene! https://www.youtube.com/watch?v=ueJ5GFLomrU

Hi Irene, The three vowels in those three words are written in the International Phonetic Alphabet as [æ] [ɑ] [ə] This website allows you to practice listening to the differences between those three vowels: http://www.ipachart.com/ Just click on the symbol to listen to it! Hope that helps!