Flytebryggen er liten.

Flytebryggen is a compound noun:

• flyte = float / floating
• brygge = pier, jetty, dock, landing stage

So flytebrygge means floating dock/pier.

With -n added at the end, flytebryggen means the floating dock/pier.

A useful thing to know about Norwegian is that compound nouns are very common, and the last part usually tells you what kind of thing it is. Here, the main noun is brygge.

The ending -en marks the noun as definite singular in Bokmål.

So:

• en flytebrygge = a floating dock
• flytebryggen = the floating dock

Unlike English, Norwegian often puts the onto the end of the noun instead of using a separate word.

The adjective has to agree with the noun in gender and number.

Here, flytebryggen is singular, and the head noun brygge is a common-gender noun in this form, so the adjective is liten.

Compare:

• en brygge er liten = a dock is small
• et hus er lite = a house is small
• bryggene er små = the docks are small

Why not lille?
Because lille is typically used in attributive definite phrases, where the adjective comes before the noun:

• den lille flytebryggen = the small floating dock

But in your sentence, the adjective comes after er, so it is predicative, and then you use:

• flytebryggen er liten

Because in Norwegian, a predicative adjective usually agrees with gender and number, but not with definiteness.

So:

• en brygge er liten = a dock is small
• bryggen er liten = the dock is small

Even though bryggen is definite, the adjective stays liten, not lille.

This is different from when the adjective comes directly before the noun:

• en liten brygge = a small dock
• den lille bryggen = the small dock

This is the normal word order for a simple Norwegian statement:

• subject + verb + complement

So here:

• Flytebryggen = subject
• er = verb
• liten = adjective/complement

It works just like English The floating dock is small.

Er means is / am / are. It is the present tense of å være = to be.

Examples:

• jeg er = I am
• du er = you are
• flytebryggen er liten = the floating dock is small

Norwegian uses er for all persons in the present tense, which is simpler than English.

In Bokmål, brygge is traditionally a feminine noun, but many feminine nouns can also be used as common-gender/masculine-style nouns.

So you may see:

• ei brygge / brygga
• en brygge / bryggen

Both can occur in Bokmål, depending on style and preference.

In your sentence, flytebryggen uses the -en definite ending, which is the common-gender/masculine-style form.

Yes, in many varieties of Norwegian, especially with more feminine forms, you could say:

• Flytebrygga er lita

This uses:

• brygga = definite feminine form
• lita = feminine form of liten

However, in standard Bokmål teaching materials, learners will very often meet:

• flytebryggen er liten

So the sentence you have is completely normal.

Yes. Liten is irregular, so it is worth memorizing.

Common forms are:

• liten = small, little
  used with common-gender singular
• lite = small, little
  used with neuter singular
• små = small
  used with plural
• lille = little/small
  often used in definite phrases before the noun

Examples:

• en liten bil = a small car
• et lite hus = a small house
• små hus = small houses
• det lille huset = the small house

Because Norwegian does not capitalize all nouns.

Only proper names and the normal beginnings of sentences are capitalized.

So:

• Flytebryggen er liten.
  Flytebryggen is capitalized only because it is the first word of the sentence.

If it appeared in the middle of a sentence, it would normally be:

• Jeg ser at flytebryggen er liten.

You would say:

• En flytebrygge er liten.

That means A floating dock is small.

Compare:

• En flytebrygge er liten. = A floating dock is small.
• Flytebryggen er liten. = The floating dock is small.

This is a useful pair because it shows both:

• the indefinite article en
• the definite ending -en on the noun