De is used with persons and most animals, singular masculine and femenine nouns and all plural nouns.
Most "de" words are masculine
De is used with nouns ending in the suffixes ing, er, heid, in and aar De is used with trees, vegetables, plants and fruits De is used with leters and numbers
Het is used with a singular neuter nouns and diminutives Het is used with names of countries or cities, when is said something specific about them Het is often used with metals, with sports... There are few rules that i got from a book
I live in Flanders and unfortunately a 'n' at the end of a word is almost never pronounced. They will pronounce the 'e' before the 'n' though. So you correctly noticed that it sounds like "eet-eh", the "eh" at the end is the only way you'll know if its plural or an infinitive verb rather than singular. Keep your ear out for it and you'll adjust. I feel your frustration though! :)