When a noun starts with a vowel, and an article ends with s letter, you combine article and noun (when you speak them, of course) and S of LES and is changing into Z. H is a vowel too. Same goes with verbs. For example: Nous avons you can't read like "Nu avon". You need to read it "Nuzavon"
They all mean "eat" - but the ending changes depending on who is doing the eating.
Mange = (I) eat ---First person singular
manges = (you) eat ---2nd person singular
mange = (he/she/it) eats ---3rd person singular
mangeons = (we) eat ---First person plural
mangez = (y'all) eat -- 2nd person plural
mangent = (they) eat ---3rd person plural