Hi Venita, 

'Het' is for neuter words. 'De' for masculine and feminine nouns.

Although there are some rules, for non-native speakers it more or less comes down to learning 'het' and 'de' words one by one. 

Here are some of the rules (there are more):

- Plural nouns = de 

- Verkleinwoorden/diminutive nouns = het

- Noun made from infinitive verb = het   

- Nouns for persons with identified gender = de (so 'de dochter' (the daughter), but 'het kind' (the child))

- Nouns for professions = de

- Letters and numbers = de 

- Nouns for languages = het

- Two syllable nouns starting with ge-/be-/ver-/ont- = het

- Words ending in -isme/-ment/-sel/-um = het

- Metals = het

- Fruits, trees, plants = de

- Words ending in -ing/-ij/-heid/-nis/-de/-te = de

- Words with a foreign origin ending in -ade/-ide/-ode/-ude/-age/-esse/-ica/-iek/-ie/-ine/-iteit/-ose/-sis/-suur/-yse = de

- Words/Names of rivers and mountains = de

Some of these rules have exceptions + There are lots of words that can't be clearly defined by any rule. You'll just have to know them. The best way would probably be regular practice and trying to memorize it as soon as you learn the noun. There are more 'de' words than 'het' words. Some Dutch learners like to view 'het' words as special words and memorize these. They use 'de' for all the others.

For some words both 'het' and 'de' are fine (like het/de doolhof (the maze)), although this sometimes leads to a different meaning of the word. 

Hope this answered your question!  

Groetjes,
Ida