The hamza is the symbol that is a عين (rħain) with no tail. It looks like this:ء The hamza is best thought of as a vowel separator.
The hamza is not a letter by itself, even though it makes a consonant sound.
The hamza is on either a ياء (yaa') or an ألف (alif) or a واو (waaw) or is by itself.
ئ / ؤ / أ / إ / ء
Arabic writing makes sense, but the hamza's carriers cannot be figured out by just hearing. One has to either know the hamza spelling rules or have seen enough Arabic words to know how a word would be spelt. And there do exist spelling rules to figure out whether and which letter a hamza should go over.
But most people don't know the rules of the hamza, and they don't need to. They can spell fine without being able to explain why.
Often people wonder why is the hamza carried by other letters at all. Here is a short explanation:
Whenever a word starts with a vowel in Arabic an alif was written.
And in the old accents, people probably didn't pronounce the hamza anywhere else in a word. for example: فائز faa-iz- meaning winner مؤمن mu'min meaning (religious) believer
were not pronounced in that manner
instead it was: faa-yiz or moomin
So if the hamza existed on a yaa' that means that the different dialects pronounced it like a yaa' instead of a hamza'. You can still hear this pronounciaction very often in Arabic dialects for many words.