Je means is.
The sentence structure is:
So the grammar is very similar to English:
The station is open today.
Unlike in some other Slavic languages, Czech normally does use the verb být (to be) in the present tense:
Because otevřená is an adjective, and it agrees with služebna.
Služebna is:
So the adjective must also be feminine singular nominative:
Examples:
That is a very common question.
On signs, Czech often uses:
This is a fixed, very common public sign style.
But when you describe a specific noun, the adjective usually agrees with that noun:
So:
Both relate to the same idea, but they are used differently.
Yes. Otevřena is also possible.
There is a difference in style:
So:
A learner will hear both, but otevřená is very safe and natural in ordinary speech.
Yes, Czech word order is flexible.
Služebna je dnes otevřená. is a very normal neutral sentence.
You can also change the order:
But the emphasis changes:
Služebna je dnes otevřená.
Neutral: the station is open today.
Dnes je služebna otevřená.
Emphasis on today.
Služebna je otevřená dnes.
Often sounds contrastive, like today (not some other day).
So the original sentence is a natural, neutral choice.
It is in the nominative singular.
That is because služebna is the subject of the sentence:
The subject of a sentence is normally in the nominative.
A rough pronunciation guide is:
A few details:
So the most important thing is: