When to use 'The' (as in thee) or 'The' (that sounds similar to "duh")

This was one of those unforgettable lessons from JP, my school principal at Vana Vani.

When I went to meet her in November last year when she had come to Chennai for her knee cap surgery operation the didactic nature in her might have triggered to ask my son something. I couldn't believe she would ask him the usage of the article "the".
What surprised me even more was my son coming up with the correct answer. I might have told him but don't know when.

Anyway here is how you use "the" correctly.

The article "the" sounding as in the word "thee" is to be used before words that begin with a vowel i.e a, e, i, o and u. The as it sounds in "duh" is to be used before words that begin with a consonant.