Dziób kajaka jest blisko brzegu rzeki.

• dziób — nominative singular; it is the subject of the sentence
• kajaka — genitive singular; it means of the kayak
• brzegu — genitive singular; it comes after blisko
• rzeki — genitive singular; it means of the river

So structurally, the sentence is roughly:

• [Dziób] = the thing being talked about
• [kajaka] = whose bow it is
• [jest blisko brzegu rzeki] = where it is

Because Polish often uses the genitive to show possession or a close of relationship.

• kajak = kayak
• dziób kajaka = the bow of the kayak

This is very normal in Polish. English often uses either of or a noun-noun structure, but Polish usually marks that relationship with a case ending.

Because blisko normally goes with the genitive.

• basic form: brzeg = bank / shore
• after blisko: blisko brzegu = near the bank/shore

This is something you usually just learn together with the word:

• blisko + genitive

For example:

• blisko domu = near the house
• blisko szkoły = near the school

Because brzeg rzeki means the bank of the river.

Again, Polish uses the genitive for an of relationship:

• brzeg = bank
• rzeka = river
• brzeg rzeki = bank of the river

So inside the bigger phrase blisko brzegu rzeki, you have:

• brzegu because of blisko
• rzeki because it depends on brzeg

Here blisko means near / close to.

It is often taught as a word that works like a preposition-like expression with the genitive:

• blisko + genitive

So:

• blisko brzegu
• blisko domu
• blisko miasta

You may also see blisko used more like an adverb in other contexts, but in this sentence the most useful thing to remember is simply:

• blisko → use the genitive

Jest is the 3rd person singular present form of być = to be.

It is needed because the sentence says what the bow’s position is:

• Dziób kajaka jest blisko brzegu rzeki
  = The bow of the kayak is near the riverbank

In standard Polish, you normally keep jest in a full sentence like this.

Literally, dziób can mean beak. But for vehicles and boats, it also means the front end or bow.

So with a kayak:

• dziób kajaka = the bow of the kayak

This kind of metaphor is common in Polish.

Yes. Polish word order is more flexible than English because case endings show grammatical relationships.

The neutral order here is:

• Dziób kajaka jest blisko brzegu rzeki.

But other orders are possible, for example to change emphasis:

• Blisko brzegu rzeki jest dziób kajaka.
• Dziób jest blisko brzegu rzeki.
  if the context already makes kajaka clear

Even so, the original version sounds natural and straightforward for a learner.

Because Polish has no articles like a or the.

So a noun like kajak or rzeka can mean:

• a kayak / the kayak
• a river / the river

The exact meaning depends on context. In this sentence, English usually translates it with the, but Polish does not need a separate word for that.

A simple learner-friendly guide:

• dziób — roughly jyoob or dzyoob, with a soft beginning
• kajaka — ka-YA-ka
• jest — yest
• blisko — BLIS-ko
• brzegu — roughly BZHE-goo
• rzeki — roughly ZHE-ki

A few useful notes:

• rz usually sounds like the s in measure, but harder
• j in Polish sounds like English y
• Polish usually stresses the second-to-last syllable, so:
  • ka-YA-ka
  • BLI-sko
  • brze-GU? No — actually BRZE-gu
  • RZE-ki

You can, but the grammar changes.

• blisko + genitive
  
  • Dziób kajaka jest blisko brzegu rzeki.

If you use bliski (close as an adjective), it usually takes the dative:

• Dziób kajaka jest bliski brzegowi rzeki.

That version is grammatical, but blisko + genitive is often the more everyday and natural pattern for location.

Usually bank is best with a river.

• brzeg rzeki = riverbank / bank of the river

But brzeg is a broader word and can also mean shore or edge depending on the context:

• brzeg morza = seashore
• na brzegu jeziora = on the shore of the lake

So here, because it is a river, riverbank is the most natural English choice.