Nouns are words in front of which you can place an article. (het) boek, (the) book (de) kast, (the) closet
The infinitive form of a verb can act as a noun: Hardlopen is goed voor je.- Running is good for one. Schaatsen is erg populair.- Ice-Skating is very popular
The names of people, companies etc. are nouns as well. They should always be written with a capital: Frits,Zaltbommel, Hema, Apple enz.