Umezeala apare lângă geam.

Because -a is the attached definite article.

• umezeală = moisture / dampness
• umezeala = the moisture / the dampness

Romanian usually puts the definite article at the end of the noun, not as a separate word like English the.

Also, umezeală is a feminine singular noun.

Apare is the 3rd person singular present tense of the verb a apărea, meaning to appear, to show up, or to form.

So here:

• umezeala = singular subject
• apare = appears / shows up / forms

That is why the verb is singular.

Because the sentence is talking about moisture showing up or forming, not simply existing.

• Umezeala apare... = Moisture appears / forms...
• Umezeala este... would mean The moisture is..., which sounds incomplete unless followed by an adjective or location in a different structure.

So apare is the natural choice if the idea is that dampness starts to become visible.

Lângă means near, next to, or by.

In this sentence:

• lângă geam = near the window / by the window

It is a very common Romanian preposition for physical closeness.

This is a very common learner question.

• geam literally means glass pane or window glass
• fereastră means window in the fuller sense

In everyday Romanian, geam is often used a bit loosely and can refer to the window area itself, especially in household contexts.

So lângă geam sounds natural.
If you said lângă fereastră, that could also be correct, but it may feel slightly different depending on context.

Because Romanian often uses a bare noun after a preposition when the location is understood generally.

So:

• lângă geam = by the window / near the window

If you wanted to make it clearly definite and specific, you could say something like:

• lângă geamul din dormitor = near the window in the bedroom

In short, geam without an article is normal here.

The given order is the most neutral one:

• Umezeala apare lângă geam.

But Romanian word order is fairly flexible. You could also say:

• Lângă geam apare umezeala.

That version gives a little more emphasis to where it appears.

So the original sentence is the standard, straightforward order: subject + verb + place expression.

They matter a lot.

• â is a Romanian vowel that does not exist naturally in English. It is pronounced deep in the center of the mouth.
• ă is like the weak vowel in the last syllable of English sofa.

So lângă is not pronounced like plain English letters would suggest. The diacritics tell you exactly which vowels to use.

Yes, it is understandable and natural enough, especially in a general description.

That said, depending on context, Romanians might also say things like:

• Apare umezeală la geam.
• Se formează condens pe geam.

The second one is especially likely if you specifically mean condensation on the window.

So your sentence is correct, but in real-life situations Romanian may choose slightly different wording depending on whether the speaker means dampness nearby or condensation on the glass.