Learn Arabic (Modern Standard): هل هو في المكتب؟

هو is the independent pronoun for 'he'. Because Arabic doesn't use the word 'is' in the present tense, we need the pronoun to tell us who the sentence is about. The sentence literally translates to '[Question marker] he in the office?'.

Does the word هل (hal) mean 'is'?

No, هل is simply a question word used to turn a regular statement into a 'Yes/No' question. The verb 'to be' (is/am/are) is completely skipped in Arabic present tense sentences. If you remove هل, you are left with the statement هو في المكتب (He is in the office).

How would I change this to ask 'Is she in the office?'

You would swap the masculine pronoun هو (huwa) for the feminine pronoun هي (hiya). The rest of the sentence remains exactly the same: هل هي في المكتب؟.

How do I pronounce في المكتب (in the office) when reading it out loud?

When reading fluidly, the vowel sound at the end of في (fī) blends into the word المكتب (al-maktab). The 'a' sound in the word for 'the' (الـ) is dropped in speech, so you pronounce the two words together as 'fil-maktab' rather than 'fee al-maktab'.