Ten katalog istnieje tylko w internecie.

Ten is the masculine singular form of the demonstrative this.

It agrees with katalog, which is a masculine singular noun:

• ten katalog = this catalogue / this catalog

A useful pattern is:

• ten for masculine nouns
• ta for feminine nouns
• to for neuter nouns

Examples:

• ten dom = this house
• ta książka = this book
• to zdjęcie = this photo

In everyday Polish, ten can sometimes feel a bit like English the, especially when referring to a specific known thing, but grammatically it still literally means this.

It is in the nominative singular.

That is because katalog is the subject of the sentence:

• Ten katalog istnieje... = This catalogue exists...

The nominative is the basic dictionary form of the noun.

Istnieje comes from istnieć, which means to exist.

So:

• Ten katalog istnieje tylko w internecie literally means This catalogue exists only on the internet

That is a bit different from jest (is). Compare:

• Katalog jest w internecie = The catalogue is on the internet
• Katalog istnieje w internecie = The catalogue exists on the internet

Istnieje emphasizes existence rather than simple location or identity.

In natural everyday Polish, if you mean something like It is only available online, people might also say:

• Ten katalog jest tylko w internecie
• Ten katalog jest dostępny tylko w internecie

So the given sentence is grammatical, but istnieje has a slightly more literal exists sense.

Istnieje is:

• 3rd person singular
• present tense
• from the verb istnieć = to exist

It matches the singular subject ten katalog.

A few forms:

• ja istnieję = I exist
• ty istniejesz = you exist
• on/ona/ono istnieje = he/she/it exists
• my istniejemy = we exist
• wy istniejecie = you (plural) exist
• oni/one istnieją = they exist

Because the preposition w usually requires the locative case when it means in.

So:

• dictionary form: internet
• locative form: internecie

That is why you get:

• w internecie = on the internet / in the internet

The same thing happens with many nouns after w:

• w domu = in the house
• w sklepie = in the shop
• w mieście = in the city

This is just a difference in how the two languages use prepositions.

English says:

• on the internet

Polish normally says:

• w internecie

So you should learn it as a fixed expression. Even though w often means in, here the natural English translation is usually on the internet.

You may see both, but lowercase is very common in modern Polish:

• internet
• w internecie

Older usage and some formal styles may use Internet with a capital letter, but lowercase is now widely accepted and very common.

Because Polish does not have articles like English a/an/the.

So Polish does not need a separate word for:

• a catalogue
• the catalogue

The noun itself, plus context, tells you what is meant.

That is one reason why ten can sometimes feel stronger than English this: Polish often uses it when pointing to a specific known item, where English might simply use the.

Tylko means only, and its position affects what is emphasized.

In:

• Ten katalog istnieje tylko w internecie

the most natural interpretation is:

• This catalogue exists only on the internet
• in other words, only in that place/form

Polish word order is fairly flexible, so other versions are possible, for example:

• Tylko w internecie ten katalog istnieje — much more marked, emphasizing only on the internet
• Ten katalog tylko istnieje w internecie — less natural in most contexts

The original sentence is the most neutral and natural arrangement.

Yes, istnieje can be tricky for English speakers.

A rough pronunciation guide is:

• ees-TNYE-ye

The difficult part is -stni- and then -eje.

Very roughly:

• ist-
• nie sounds like nye
• je sounds like ye

So:

• istnieje ≈ ees-TNYE-ye

You do not need to pronounce every letter separately in an English-like way. Try to say it smoothly as one word.

Yes, in many contexts Polish also uses:

• online

For example:

• Ten katalog jest dostępny tylko online = This catalogue is available only online

But w internecie is very natural and fully standard Polish.

The difference is mostly style:

• w internecie = standard, neutral
• online = very common too, a bit more modern/international in feel

Yes, katalog is masculine singular.

One clue is that many Polish nouns ending in a consonant are masculine, and katalog ends in -g.

You can also tell from the demonstrative:

• ten katalog

If it were feminine, you would expect ta If it were neuter, you would expect to

So the agreement shows the gender clearly.

The literal meaning of ten katalog is this catalogue, but depending on context, English may translate it more naturally as the catalogue.

That happens because Polish has no articles, and demonstratives are sometimes used where English would simply use the for a known item.

So depending on context, possible translations might be:

• This catalogue exists only on the internet
• The catalogue exists only on the internet
• This catalogue is only available online — a freer, more natural translation in some situations

The exact best translation depends on what the speaker is trying to emphasize.