"هٰذِهِ الْغُرْفة جَميلة."
Translation:This room is pretty.
Well, the verb never gets an article (does it in English?).
Anyway, as a rough guide, here are two sentences below and their Arabic counter part:
1. This is a beautiful room: هذه غرفة جميلة.
2. This room is beautiful: هذه الغرفة جميلة.
One can say also (This is the beautiful room), and it will sound as it is emphatic in Arabic: هذه هي الغرفة الجميلة.
I can go deeper into grammar if you want to but maybe as a beginner you wouldn't want that and rather focus on the vocabulary :)
This room: هذه الغرفة - this is the subject of the sentence. In Arabic, in nominal sentences (sentences that start with a noun), the subject is always defined with (AL), except for very rare special cases.
The predicative, جميلة is an adjective. The predicative in nominal sentences does not come defined with (AL).
In English, you might divide the sentence to "subject" and "predicative" as: Whatever comes before (is) is the subject, and whatever comes after (is) is the predicative. The predicative is that part of the sentence that tells information about the subject, and hence you would use (is) - or generally the verb "to be" to connect the sentence together.
In Arabic, there are 2 types of sentences, Nominal ad Verbal. Putting the Verbal type aside because it's not the case here; The nominal sentence is a sentence that starts with a noun and can be completed without any verbs; We don't need the verb "to be" or (is) to connect a full sentence in Arabic (unless it comes to the past tense). The thing that plays the rule here is the definite article (AL). The examples I've posted above in the previous response might elaborate further how adding (AL) and removing (AL) changes the translation in English.
This is a pretty room = هذهِ غُرْفَةٌ جَميلة (háδihi ğurfatun jamílah) [δ=TH as in This].
Notice the role of the definite article الـ in the sentence. Adding that to غرفة (a room) makes it الغرفة (the room). Once it is added and we have هذه (this), then the two get merged like one entity in meaning to mean: This room. Removing the definite article from (room), would make it (this is A room).
In case we would like to say something like: This is THE room which is emphatic style, that would be: هذه هي الغرفة (háδihi hiya al-ğurfah). The pronoun (hiya) means "she" (because "room" is feminine in Arabic) and it is added to separate هذه and الغرفة and consequently adding emphasis to the sentence.