Chcę się upewnić, że ul jest zamknięty.

Literally, it is something like I want to make myself sure. In natural English, that becomes I want to make sure.

• chcę = I want
• się upewnić = to make sure / to become sure

So the whole first part, Chcę się upewnić, is a very natural way to say I want to make sure.

Because upewnić się is the standard dictionary form of the verb phrase. It is a reflexive verb expression.

In Polish, many verbs are used with się, and you often just have to learn them that way. Here:

• upewnić się = to make sure
• without się, upewnić is not normally used in the same everyday sense

So się is not optional here. You should learn the whole chunk upewnić się as one unit.

Because it comes after chcę.

In Polish, after verbs like chcieć (to want), you usually use an infinitive:

• Chcę iść = I want to go
• Chcę sprawdzić = I want to check
• Chcę się upewnić = I want to make sure

So upewnić is in the infinitive because it depends on chcę.

This is about aspect, which is very important in Polish.

• upewnić się = perfective
• upewniać się = imperfective

Here, upewnić się is used because the speaker wants to achieve a result: to confirm something once, successfully.

So:

• Chcę się upewnić... = I want to make sure...
• Chcę się upewniać... would sound unusual here, because it suggests an ongoing or repeated process rather than one completed check

In this sentence, the perfective verb is the natural choice.

Że introduces a clause meaning that:

• Chcę się upewnić, że... = I want to make sure that...

It connects the main idea to the statement being confirmed.

So:

• że ul jest zamknięty = that the hive is closed

This is very common in Polish after verbs of saying, knowing, believing, or making sure.

Sometimes yes, but the meaning shifts slightly.

• upewnić się, że... = make sure that something is true
• upewnić się, czy... = check whether / if something is true

So:

• Chcę się upewnić, że ul jest zamknięty sounds like the speaker wants confirmation of the fact
• Chcę się upewnić, czy ul jest zamknięty sounds more like I want to check whether the hive is closed

In many real situations, both can be possible, but że matches the idea of being sure of a fact, while czy focuses more on checking.

Here, ul means beehive.

This can confuse learners because ul. with a dot is an abbreviation of ulica (street) in addresses.

So:

• ul = beehive
• ul. = abbreviation for street

In your sentence, because there is no dot and the meaning is already clear from context, ul means beehive.

Because ul is the subject of the clause, so it is in the nominative case.

The clause is:

• ul jest zamknięty = the hive is closed

Here:

• ul = subject
• subjects normally take the nominative

You would see ula in other cases, for example the genitive:

• Nie ma ula = There is no hive

But in this sentence, nominative ul is correct.

Zamknięty is an adjective meaning closed, and it agrees with ul.

Polish adjectives must match the noun in:

• gender
• number
• case

Ul is:

• masculine
• singular
• nominative

So the adjective also appears in the masculine singular nominative form:

• zamknięty

If the noun were different, the adjective would change too. For example:

• drzwi są zamknięte = the door / doors are closed
• furtka jest zamknięta = the gate is closed

In this sentence, jest should normally be included.

• ul jest zamknięty = the hive is closed

In present-tense Polish, the verb to be is often omitted in some styles only when talking about identity or classification, especially in informal speech, but with predicate adjectives like zamknięty, you normally keep jest.

So:

• ul zamknięty is not a normal full sentence here
• ul jest zamknięty is the standard form

Not completely. Polish word order is more flexible than English, because endings do a lot of the grammatical work.

The neutral order here is:

• Chcę się upewnić, że ul jest zamknięty.

But you could change the order for emphasis, for example:

• Chcę się upewnić, że zamknięty jest ul.

That sounds marked or emphatic, not neutral. A learner should stick with the original version unless there is a special reason to emphasize something.

A rough English-style guide:

• Chcę ≈ h-tsen
• się ≈ shyeng or shenh depending on speech style
• upewnić ≈ oo-PEV-nyeech
• że ≈ zheh
• ul ≈ ool
• jest ≈ yest
• zamknięty ≈ zam-kNYEN-tih

A few useful notes:

• ch sounds like a strong h
• ę is a nasal vowel; learners often simplify it, which is normal at first
• ń is a soft n
• rz in że sounds like zh in measure

If you want to sound natural, the main stress is usually on the second-to-last syllable of each word:

• u-PEW-nić
• zam-KNIĘ-ty

Yes, it is natural and correct.

It sounds like something someone might say when checking something practical:

• Chcę się upewnić, że ul jest zamknięty.

A close alternative would be:

• Chcę sprawdzić, czy ul jest zamknięty.

That version is a bit closer to I want to check if the hive is closed, while your original sentence is closer to I want to make sure that the hive is closed. Both are natural, but they are not exactly identical in nuance.