The negation in the indicative is formed by δεν+verb. It is in fact easier than the English negation where you also need to employ the auxiliary to do. Both words are needed because one is the negation particle and the other the verb itself.
I googled 'negation in modern greek' and this was listed second: http://www.asteri.ws/en/gramm1/neg-en.html I think you'll find it helpful (and while it's a bit extensive you can just take what you need for now from it). Also check https://en.wikipedia.org/wiki/Modern_Greek_grammar#Negation