To słownictwo jest ważne, jeśli chcesz mówić poprawnie.

No. Polish does not have articles like a and the.

Here to is a demonstrative, meaning this. So to słownictwo means this vocabulary.

You could also say Słownictwo jest ważne, which would mean Vocabulary is important or The vocabulary is important, depending on context. Adding to makes it more specific: this vocabulary.

Not quite.

• słownictwo = vocabulary, meaning a set/system of words
• słowa = words, meaning individual words

So słownictwo is a collective noun. Even though vocabulary contains many words, grammatically it behaves as a singular noun in Polish.

That is why the sentence uses singular forms like jest and ważne.

Because adjectives in Polish must agree with the noun in gender, number, and case.

słownictwo is:

• singular
• neuter
• here in the nominative

So the adjective must also be neuter singular nominative:

• masculine: ważny
• feminine: ważna
• neuter: ważne

Since the noun is słownictwo, the correct form is ważne.

It is in the nominative case.

Why? Because słownictwo is the subject of the sentence: it is the thing that is important.

So:

• to słownictwo = subject
• jest ważne = predicate

This is the basic dictionary form of the noun.

Because Polish often leaves out subject pronouns when they are clear from the verb ending.

chcesz already means you want. The ending -sz shows that it is 2nd person singular.

So:

• chcesz = you want

You could add ty for emphasis:

• jeśli ty chcesz mówić poprawnie...

But in a normal sentence, that usually sounds unnecessary.

Because after chcieć (to want), Polish normally uses an infinitive to say what someone wants to do.

So:

• chcesz = you want
• mówić = to speak

Together:

• chcesz mówić = you want to speak

This works very much like English:

• I want to learn
• Chcę się uczyć

This is about aspect.

• mówić is imperfective
• powiedzieć is perfective

In this sentence, the meaning is general and ongoing: to speak correctly as a skill or habit. For that, Polish uses mówić.

If you used powiedzieć, it would sound more like to say something correctly once or to manage to say it correctly.

So:

• mówić poprawnie = speak correctly in general
• powiedzieć poprawnie = say something correctly

Because poprawnie is an adverb, and it describes how you speak.

• poprawny = correct → adjective
• poprawnie = correctly → adverb

Here it modifies the verb mówić:

• mówić jak? → poprawnie
• speak how? → correctly

If you used poprawny, you would need a noun:

• poprawny tekst = a correct text
• poprawna odpowiedź = a correct answer

Yes, jeśli means if.

You can also use jeżeli. The meaning is basically the same. The difference is mostly one of style:

• jeśli = very common, neutral
• jeżeli = a bit more formal or careful-sounding

So both are correct:

• Jeśli chcesz mówić poprawnie...
• Jeżeli chcesz mówić poprawnie...

In everyday use, jeśli is extremely natural.

Yes. In Polish, a subordinate clause introduced by words like jeśli, że, ponieważ, kiedy is normally separated by a comma.

So the comma in:

To słownictwo jest ważne, jeśli chcesz mówić poprawnie.

is correct and expected.

This is one place where Polish punctuation is often stricter than English learners expect.

Yes, Polish word order is more flexible than English word order.

For example, you could also say:

Jeśli chcesz mówić poprawnie, to słownictwo jest ważne.

That still works. The basic meaning stays the same, but the emphasis changes slightly. Putting the if-clause first makes the condition more prominent.

Still, the original sentence sounds very natural and straightforward.

Yes.

• To słownictwo jest ważne = This vocabulary is important
• Słownictwo jest ważne = Vocabulary is important / The vocabulary is important

Leaving out to makes the sentence more general. Keeping to points to a specific vocabulary set already known from context.

So both are grammatical, but they do not feel exactly the same.

A rough guide:

• to ≈ toh
• słownictwo ≈ swov-NEETS-tvo
• jest ≈ yest
• ważne ≈ VAZH-neh
• jeśli ≈ YESH-lee with a softer sh
• chcesz = difficult for English speakers; ch is like the sound in German Bach, not like English ch
• mówić ≈ MOO-veech
• poprawnie ≈ po-PRAV-nye

A few useful sound notes:

• ł sounds like English w
• w sounds like English v
• ó sounds like oo
• Polish stress is usually on the second-to-last syllable

So:

• słow-NIC-twoo? No — better: słow-NIC-two is not right
• the real stress is słow-NIC-two? Actually the standard stress is on the middle syllable: słow-NICT-wo? No, the practical learner-friendly version is swov-NEETS-tvo

The main thing to remember is the general stress pattern and the special consonants.