Vowels: Monophthongs vs. Diphthongs

What is the difference between monophthongs and diphthongs?
Monophthongs are the individual sounds made by the resonant space in the mouth. The air escapes the mouth with no obstruction. They vibrate the vocal cords creating what’s referred to as voiced sounds.
Diphthongs are created by two vowel sounds together. So, they start with a mouth position and end up with a different one. The sound created by this glide between the two sounds is what makes the sound of diphthongs.