Ten sweter jest za ciasny.

Ten means this and agrees with the noun sweter.

Because sweter is:

• masculine
• singular
• in the nominative case (the basic dictionary form, used here because sweter is the subject)

the correct form is ten.

Compare:

• ten sweter = this sweater
• ta koszulka = this T-shirt
• to ubranie = this piece of clothing / this garment

Sweter is simply the Polish word for sweater. It is a masculine noun.

Its nominative singular form is sweter, and that is the form used here because it is the subject of the sentence:

• Ten sweter = this sweater

Other forms change depending on case, for example:

• Nie mam tego swetra = I don’t have this sweater
• Przyglądam się temu swetrowi = I am looking at this sweater

But in this sentence, the basic form sweter is correct.

Jest means is.

The sentence has the structure:

• Ten sweter = subject
• jest = is
• za ciasny = too tight

So it works like English:

• This sweater is too tight.

In Polish, the verb to be is often omitted in the present tense only in some informal contexts? Actually, with this kind of normal descriptive sentence, jest is usually kept:

• Ten sweter jest za ciasny.

Dropping jest here would sound incomplete or unnatural for standard Polish.

Here za means too.

So:

• za ciasny = too tight
• za duży = too big
• za mały = too small
• za drogi = too expensive

This is a very common Polish pattern:

• za + adjective/adverb

Examples:

• To jest za trudne. = It is too difficult.
• Mówisz za szybko. = You speak too fast.

Do not confuse this za with other meanings of za, such as:

• behind
• for
• in exchange for

Its meaning depends on context.

Ciasny means tight.

The ending -y is the masculine singular nominative form of the adjective, because it agrees with sweter, which is masculine singular.

Compare:

• ten sweter jest za ciasny = this sweater is too tight
• ta koszulka jest za ciasna = this T-shirt is too tight
• to ubranie jest za ciasne = this clothing/item is too tight

So the adjective changes depending on the gender and number of the noun.

Ciasny is an adjective, used to describe a noun:

• sweter jest ciasny = the sweater is tight

Ciasno is usually an adverb or predicative form, used in different structures:

• Tu jest ciasno. = It is cramped here.
• Mam ciasno w butach. = My shoes are tight / I feel cramped in my shoes.

So in Ten sweter jest za ciasny, you need the adjective ciasny because it describes sweter.

Polish often does not need an extra subject pronoun like it if the noun itself is already present.

English says:

• This sweater is too tight.

Polish also just says:

• Ten sweter jest za ciasny.

There is no need for a separate word meaning it, because ten sweter already tells you what is being talked about.

Yes, Polish word order is more flexible than English, but the neutral, most natural version here is:

• Ten sweter jest za ciasny.

Other orders are possible for emphasis, for example:

• Za ciasny jest ten sweter.
• Ten sweter za ciasny jest. — possible, but much less neutral and more marked

A learner should usually stick with:

• subject + jest + description

That will sound the most natural in most situations.

This is an important difference:

• za ciasny = too tight
  -> it is tighter than is acceptable or comfortable

• bardzo ciasny = very tight
  -> strong description, but not necessarily excessive

Examples:

• Ten sweter jest bardzo ciasny. = This sweater is very tight.
• Ten sweter jest za ciasny. = This sweater is too tight.

So za expresses a problem or excess.

A simple learner-friendly approximation is:

• ten ≈ ten
• sweter ≈ SVEH-ter
• jest ≈ yest
• za ≈ za
• ciasny ≈ CHAS-nih or CHAS-ny

A few helpful notes:

• sw in sweter is pronounced with a clear s + v sound, not like English sw in sweater
• j in Polish sounds like English y in yes
• ci before a vowel often sounds like a soft ch-like sound
• sz sounds like English sh

Since ciasny contains a soft consonant, its exact pronunciation may take practice. Listening to native audio is especially helpful here.

It is neutral and natural in both everyday speech and normal writing.

It is not especially formal, but it is completely correct standard Polish. You could say it:

• in a shop
• at home
• while talking to a friend
• while describing clothing in writing

So it is a good standard sentence to learn.

Yes. Zbyt ciasny also means too tight.

Compare:

• Ten sweter jest za ciasny.
• Ten sweter jest zbyt ciasny.

Both are correct, but there is a slight difference in feel:

• za ciasny is very common in everyday speech
• zbyt ciasny can sound a little more formal or careful

Both are useful, but za ciasny is probably the more conversational choice.

The demonstrative and adjective must agree with the noun.

Examples:

Feminine singular

• Ta koszulka jest za ciasna. = This T-shirt is too tight.

Neuter singular

• To ubranie jest za ciasne. = This garment/item is too tight.

Masculine personal plural

• Ci mężczyźni są za ciasno ubrani. = These men are dressed too tightly / in clothes that are too tight.
  This is a different structure, but it shows plural agreement.

Non-masculine-personal plural

• Te spodnie są za ciasne. = These trousers are too tight.

So when the noun changes, words like ten / ta / to / te and ciasny / ciasna / ciasne also change.