Its a grammar thing, also helps with understanding the roots of the words. This is why in greek there are ''homophone'' letters (same-sound letters like o&ω, ε&αι, ι&υ&η&οι&ει).
If you learn the homophone letters and a few diphthongs (like the English ph) (all together there are about 10, no more) then the Greek is the most easy language to read.(Its still a pain to write as you are not sure which homophone letter to use).
Its very easy to read since every letter is always pronounced in the same way, there are no silent letters, and you enunciate where there is a '' ' '' on a vowel in the word
ex. μαμά its mamA (it means mom).