ביום שלישי אני קמה מוקדם, כי יש לי פגישה חשובה במשרד.

ב־ means on / in, so ביום שלישי literally means on Tuesday.

• יום שלישי = Tuesday
• ביום שלישי = on Tuesday

In Hebrew, time expressions often use a preposition like ב־ where English may or may not use one.

ביום is made of:

• ב־ = in / on
• יום = day

So ביום literally means on the day of or during the day of, but in normal English translation here it is simply on.

Because the speaker is female.

In the present tense, Hebrew verbs agree with gender and number:

• אני קם = I get up / I am getting up (male speaker)
• אני קמה = I get up / I am getting up (female speaker)

Hebrew does not usually mark person in the present tense as clearly as in English, but it does mark gender and number.

It can mean either, depending on context.

Hebrew present tense often covers both:

• a general/habitual meaning: I get up early
• an ongoing meaning: I am getting up early

In this sentence, because of ביום שלישי and the reason that follows, it most naturally sounds like a habitual or scheduled action: On Tuesday I get up early...

Because מוקדם here functions like an adverb: early.

Although מוקדם / מוקדמת can also be adjectives meaning early, after verbs like לקום it is very common to use מוקדם in this adverb-like way:

• אני קמה מוקדם = I get up early

So even though the speaker is female, מוקדם stays the usual form here.

כי means because.

It introduces the reason:

• אני קמה מוקדם = I get up early
• כי יש לי פגישה חשובה במשרד = because I have an important meeting at the office

So the whole sentence has the structure:

[main statement] + כי + [reason]

Hebrew often expresses possession with יש ל־:

• יש = there is / there exists
• לי = to me

So יש לי פגישה literally means there is a meeting to me, but idiomatically it means I have a meeting.

This is a very common Hebrew structure:

• יש לי ספר = I have a book
• יש לה זמן = she has time
• יש לנו שאלה = we have a question

לי is:

• ל־ = to / for
• ־י = me

So לי means to me or for me.

In יש לי פגישה, it marks the person who has something.

In Hebrew, adjectives usually come after the noun, and they must agree with it in gender and number.

• פגישה is a feminine singular noun
• so the adjective must also be feminine singular: חשובה

That is why:

• פגישה חשובה = an important meeting

Compare:

• ספר חשוב = an important book (masculine singular)
• פגישה חשובה = an important meeting (feminine singular)

A few clues help:

1. Many nouns ending in ־ה are feminine.
2. The adjective after it is חשובה, which is feminine singular.
3. You learn noun gender as part of the word.

So here the agreement confirms it:

• פגישה
  • חשובה

במשרד means in the office or at the office.

It combines:

• ב־ = in / at
• ה = the
• משרד = office

When ב־ joins ה־, they contract:

• ב + המשרד → במשרד

This is very common in Hebrew:

• בבית = in the house / at home
• בספר = in the book
• במשרד = in the office

Because the sentence means an important meeting, not the important meeting.

• פגישה חשובה = an important meeting
• הפגישה החשובה = the important meeting

But במשרד includes the office, because ב־ + ה־ + משרד becomes במשרד.

So the sentence specifically says:

• a meeting
• at the office

In Hebrew, a comma before כי is common when it introduces a reason clause, especially in a full written sentence like this one.

So:

• אני קמה מוקדם, כי יש לי פגישה חשובה במשרד.

looks natural and standard.

In less formal writing, people may sometimes omit commas, but here the comma helps separate the main clause from the explanation.

Yes, Hebrew word order is somewhat flexible, but the original sentence is very natural.

Original:

• ביום שלישי אני קמה מוקדם, כי יש לי פגישה חשובה במשרד.

You could also say:

• אני קמה מוקדם ביום שלישי, כי יש לי פגישה חשובה במשרד.

Both are understandable. The original puts ביום שלישי first for emphasis on the time: On Tuesday...

Yes.

The days of the week in Hebrew are often numbered:

• יום ראשון = first day = Sunday
• יום שני = second day = Monday
• יום שלישי = third day = Tuesday

So שלישי means third. That is why יום שלישי is Tuesday.