Theory:
The alphabet used for English has 5 vowels,
A, E, I, O, and U
and there are at least 3 ways in which each of these can be pronounced:
The long vowel sound.
The short vowel sound.
The silent vowel sound.
Let's look at what each of these mean.
The first vowel A has a name, and the sound of the name is called the long vowel sound, such as in words like NAME.
The same vowel A also has a typical sound associated with it, the sound od A as in cAt,
This sound is the short vowel sound for the letter A.
The third case is that in many words, the vowel A can be silent, as in meAt.
The words below give the long and short vowel sounds for the five vowels:

Long vowel sounds are called long because the sound is held for a longer period of time, and is completely different from the short vowel sound. It is not just a longer version of the short vowel sound.
A vowel can either have the long sound or the short sound, but it can also be silent:
meAt, where the A is silent.
Silent vowels do one of two things:
They eother do nothing and just appear in many words,
or they appear and affect how other vowels sound:
cAp uses the short vowel sound for the A
cApE uses the long vowel sound for the A because the E at the end of the word is not only silent, but changes the sound of the A before it.
The rule is:
When a vowel and consonant are followed by an e', the e' is almost always silent, but it causes the preceding vowel to be long.
ate,
plane,
bite,
nine,
rope,
cube,
A vowel at the end of a syllable is almost always long:
we,
he,
she,
go,
Many words have two vowels together,
mEAt
gOAT
and when that happens, very often the first vowel is long and the second vowel is silent.
Many words have the O vowel, but it sounds like the short U sound:
mOney
sOme
lOve
The O here sounds like the short U sound.