To make the plural form of a noun you have to add "er" to the singular form.
Example: Fugl (bird) ---> Fugler (birds)
Am I right? Thanks a lot.
You are right in the case of fugl, but single syllable neuter nouns do not take the er ending.
Jeg ser mange dyr!
Det finnes to ord.
Bygda har ti hus.
Then there is the case for the definite article.
The bird — fuglen
The birds — fuglene
The children — barna
there is also the case of names like sykkel, which becomes sykler losing "ke".
and names ending in -er in singular usually only take an -e for the undefinite plural, like lærer (teacher), plural lærere (teachers)
Usually, but it depends entirely on the noun. Some take no suffix at all, some have a sound change.
Masculine and feminine nouns gets this suffix, and some develop a sound change. En fot - føtter. There are of course exceptions... there's always exceptions: en mann - menn.
Neuter nouns do often not have this plural suffix (et hus - (flere) hus), but there are some exceptions: et eple - epler.