אנחנו מתרגשות לפני ההופעה, כי זאת הפעם הראשונה שאנחנו שרות שיר מול קהל.

Because Hebrew present-tense forms agree with the gender and number of the subject.

• אנחנו can mean we for any group.
• מתרגשות and שרות are feminine plural, so they tell you the speakers are an all-female group.
• If the group were male or mixed, Hebrew would normally use masculine plural:
  • אנחנו מתרגשים
  • אנחנו שרים

So the gender information comes from the verb form, not from אנחנו itself.

In Hebrew, the present tense is built from forms that often look adjective-like, because historically they are participles.

So מתרגשות can behave a bit like both:

• grammatically, it is the present-tense form of להתרגש
• in the sentence, it functions like are excited / get excited

That is why Hebrew learners often feel that present-tense verbs look like adjectives. In practice, here you should treat אנחנו מתרגשות as the verbal idea we are excited.

Because Hebrew usually does not use a separate present-tense form of to be.

So:

• אנחנו מתרגשות = we are excited
• אנחנו שרות = we are singing / we sing

In the present tense, Hebrew normally leaves out am / is / are.
In past and future, forms of להיות can appear when needed.

זאת means this or this is here.

In the pattern זאת הפעם הראשונה..., Hebrew is basically saying:

• this is the first time...

It is feminine because it points forward to פעם, and פעם is a feminine noun.

You could also often hear or see זו הפעם הראשונה.
Both זו and זאת are used for feminine this.

Because in Hebrew, when a noun is definite, its adjective also has to be definite.

Here:

• פעם = time / occasion
• ראשונה = first
• הפעם הראשונה = the first time

So both words take ה־:

• הפעם
• הראשונה

This is normal Hebrew agreement with definite noun + adjective/ordinal.

שאנחנו is a combination of:

• ש־ = that / which / when
• אנחנו = we

So שאנחנו שרות means something like:

• that we sing
• that we are singing

This ש־ is extremely common in Hebrew and introduces subordinate clauses.

Other common examples:

• שאני = that I
• שהוא = that he
• שהיא = that she

Because the sentence is describing an action performed by the subject we, inside a full clause:

• שאנחנו שרות שיר = that we are singing a song

Hebrew often uses a full ש־ clause after expressions like the first time.

So this structure is very natural:

• זאת הפעם הראשונה שאנחנו שרות...

An infinitive structure is possible in other sentences, but it would be built differently. For example, you could say something more like this is our first time singing..., but that is not the structure used here.

לפני means before.

So:

• לפני ההופעה = before the performance

The noun has ה־ because it refers to a specific performance, not just any performance.

Compare:

• לפני הופעה = before a performance
• לפני ההופעה = before the performance

So the phrase is straightforward: preposition לפני + noun phrase ההופעה.

מול literally means opposite / facing / in front of.
With people or an audience, it naturally means in front of.

So:

• מול קהל = in front of an audience

There is no ה־ on קהל because the meaning is general, not a specific known audience.

Compare:

• מול קהל = in front of an audience
• מול הקהל = in front of the audience

כי is a very common Hebrew word meaning because.

Here it introduces the reason:

• אנחנו מתרגשות... כי...
• We are excited... because...

It is one of the most common ways to connect two clauses in Hebrew.

Other possibilities exist, such as:

• מפני ש־ = because
• בגלל ש־ = because

But כי is simple, common, and very natural here.

Yes, but the meaning about the speakers would change.

This sentence uses feminine plural:

• מתרגשות
• שרות

That means the speakers are female.

If you changed it to masculine plural:

• אנחנו מתרגשים לפני ההופעה, כי זאת הפעם הראשונה שאנחנו שרים שיר מול קהל

that would usually mean the group is male or mixed.

So the choice is grammatical agreement, not just style.