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.