Ta marynarka pasuje do szarych spodni.

Because marynarka is a feminine noun in Polish. The demonstrative ta means this for feminine singular nouns.

So:

• ten = masculine
• ta = feminine
• to = neuter

Since marynarka is feminine, you say ta marynarka.

Not quite. Marynarka usually means a blazer, suit jacket, or sport coat rather than a general outdoor jacket.

For example:

• marynarka = blazer / suit jacket
• kurtka = jacket / coat for outdoor wear

So in this sentence, marynarka sounds more like a clothing item you would match with trousers, not a winter jacket.

Because the subject is ta marynarka, which is singular.

Polish verbs agree with the subject:

• Ta marynarka pasuje = This blazer matches
• Te marynarki pasują = These blazers match

Even though spodni refers to trousers, it is not the subject here. It is part of the phrase do szarych spodni.

Pasować do is a very common expression meaning:

• to match
• to go with
• to suit

In clothing contexts, it often means that one item looks good with another.

So pasować do is best learned as a set phrase:

• pasować do czegoś = to go with something / match something

Because pasować often combines with do when you want to say that one thing matches another.

So the pattern is:

coś pasuje do czegoś
= something goes with something

Examples:

• Ta koszula pasuje do spodni.
• Te buty pasują do sukienki.

Also, do requires the genitive case, which is why the next words change form.

Because after do, Polish uses the genitive case.

The basic form is:

• szare spodnie = gray trousers

But after do, both words change:

• do szarych spodni

Here is what happens:

• szare → szarych
• spodnie → spodni

So this is a case change caused by the preposition do.

Because spodnie is one of those Polish nouns that exist only in the plural. This is called pluralia tantum.

Even when talking about one pair of trousers, Polish still uses plural grammar:

• te spodnie są nowe = these trousers are new

Not:

• to spodnie jest nowe

Other similar nouns include:

• drzwi = door
• nożyczki = scissors

So spodnie is grammatically plural even when it refers to one item.

Yes. Pasować can mean several related things, depending on context:

• match / go with
• fit
• suit

For example:

• Ta marynarka pasuje do szarych spodni.
  = This blazer goes with the gray trousers.

• Ta marynarka mi pasuje.
  = This blazer fits me / suits me.

So context is very important. In your sentence, because of do szarych spodni, the meaning is clearly goes with / matches.

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

The most neutral version is:

• Ta marynarka pasuje do szarych spodni.

But you could also say:

• Do szarych spodni pasuje ta marynarka.

That version puts more emphasis on the gray trousers.

So the meaning stays very similar, but the emphasis can shift.

Because the adjective and noun agree with each other in case and number.

Here:

• szarych = adjective in genitive plural
• spodni = noun in genitive plural

They form one noun phrase: of gray trousers / with gray trousers after do.

This kind of agreement is very important in Polish. The adjective changes its form to match the noun.

Yes, it sounds natural. It is a normal way to say that one clothing item matches another.

You might also hear similar sentences like:

• Ta koszula pasuje do tych spodni.
• Te buty pasują do tej sukienki.

So the structure is very useful and worth memorizing:

• [item] pasuje do [item in genitive]