People often underestimate the importance of phonetics, they think if they know some grammar and some words they know how to speak the language. Unfortunately, when we can't say the words correctly it makes it difficult for other people to understand us AND, surprisingly, it makes it harder for US to understand what other people say. We can't recognise the correct sounds if we say them in a wrong way. So, let's start by learning the vowels - sounds that correspond to letters A, E, I, O, U.
Vowel sounds are produced with a relatively open vocal tract, the air can pass from your lungs, through your mouth, and out into the world. There are 11 vowel sounds in English you need to learn:
Note that these are the standard vowel phonemes of English and there may be variations and different realisations of these sounds depending on the dialect or accent.
Now listen to a native English speaker say the sounds. Make sure you can hear that each sound is different from the others.