Moram izuti čizme prije nego što uđem u sobu.

After morati (to have to / must), Croatian normally uses the infinitive of the main verb.

• moram = I must / I have to
• izuti = to take off (footwear)

So:

• Moram izuti čizme = I have to take off my boots

Using izujem here would be wrong, because izujem is a finite verb form (I take off), not an infinitive.

Izuti specifically means to take off footwear: shoes, boots, socks, slippers, etc.

So it is more specific than skinuti, which is a general verb meaning to take off / remove.

Examples:

• izuti čizme = take off boots
• izuti cipele = take off shoes
• skinuti kaput = take off a coat
• skinuti sat = take off a watch

You may hear skinuti čizme too, and people will understand it, but izuti is the more natural, precise choice for footwear.

Because čizme is the direct object of izuti, and with this verb the object is in the accusative case.

The noun is čizme (boots), plural. For this noun, the nominative plural and accusative plural look the same:

• nominative plural: čizme
• accusative plural: čizme

So even though the form does not change, the case is still accusative here because the boots are what is being taken off.

Prije nego što means before when introducing a whole clause.

It links two actions:

• Moram izuti čizme = I have to take off my boots
• prije nego što uđem u sobu = before I enter the room

So the structure is:

• prije nego što + clause

This is very common in Croatian.

You can think of it as:

• prije = before
• nego što = than / that (part of a fixed linking expression here)

As a full connector, it simply means before.

This is about verb aspect.

• ući = to enter / to go in → perfective
• ulaziti = to be entering / to enter repeatedly → imperfective

In the sentence, the speaker means the single completed action of entering the room, so Croatian uses the perfective verb:

• prije nego što uđem u sobu = before I enter the room

If you said ulazim, it would sound more like while I am entering or refer to a repeated/ongoing action, which is not the idea here.

This is very normal in Croatian.

After conjunctions like prije nego što, Croatian often uses a present-tense form of a perfective verb to refer to a future completed action.

So:

• uđem literally looks like present tense
• but here it means something like before I enter / before I go in

This is one of the things English speakers often need to get used to. Croatian does not always use a separate future form where English might expect one.

So prije nego što uđem is more natural than something like prije nego što ću ući, which would not be correct here.

Here it is accusative: u sobu.

With u, Croatian uses:

• accusative for movement into something
• locative for location inside something

So:

• u sobu = into the room / entering the room
• u sobi = in the room

Because the verb uđem expresses movement into the room, accusative is required:

• uđem u sobu = I enter the room

Compare:

• Ja sam u sobi. = I am in the room.
• Ulazim u sobu. = I am entering the room.

Croatian often leaves out possessive words like my, your, his, etc. when the meaning is obvious from context.

So:

• Moram izuti čizme naturally means I have to take off my boots

Since it is obvious that people usually take off their own boots, Croatian does not need to say moje čizme unless the speaker wants emphasis or contrast.

Compare:

• Moram izuti čizme. = I have to take off my boots.
• Moram izuti moje čizme, ne tvoje. = I have to take off my boots, not yours.

So leaving out moje is completely normal.

In everyday language, some speakers may shorten expressions in certain contexts, but the standard and safest form here is:

• prije nego što uđem u sobu

For learners, it is best to use the full expression prije nego što.

That will sound natural and correct in standard Croatian.

Croatian usually does not need subject pronouns, because the verb ending already shows who the subject is.

• moram clearly means I must
• uđem also clearly means I enter

So ja is unnecessary unless you want emphasis:

• Moram izuti čizme... = neutral, natural
• Ja moram izuti čizme... = I have to take off the boots (emphatic)

This is very common in Croatian and other Slavic languages.

The sentence as given is natural and neutral:

• Moram izuti čizme prije nego što uđem u sobu.

Croatian word order is fairly flexible, but changing it can change the emphasis.

For example:

• Prije nego što uđem u sobu, moram izuti čizme.
  = Before I enter the room, I have to take off my boots.

This version is also correct, but it puts more focus on the time relationship.

So the original order is a normal, straightforward way to say it.

The basic dictionary form is ući (to enter / to go in).

Uđem is a present-tense form, first person singular, from that verb.

A few useful forms:

• ući = to enter
• uđem = I enter
• uđeš = you enter
• uđe = he/she/it enters

This verb is irregular enough that learners usually need to memorize it.

Then Croatian would often prefer the imperfective verb in the second clause:

• Moram izuti čizme prije nego što ulazim u sobu would not be the most natural choice in many contexts, but for repeated habit Croatian would more naturally rephrase the idea, for example:
• Moram izuvati čizme prije ulaska u sobu in some contexts, or simply keep the standard sentence if the general rule is understood.

For most learners, the important point is this:

• izuti and ući are perfective
• they fit well when talking about a single completed action or a normal sequence of events

So in your sentence, the perfective forms are exactly what you would expect.