Learn Hardcore Spanish (Latin America): La jefa firmará el acuerdo mañana. - The boss will sign the agreement tomorrow.

acuerdo: an agreement or accord (can be formal or informal), often the result of negotiation.
contrato: a contract (a legally binding document). Depending on context, you might also see convenio (formal agreement/MOU).

It’s the feminine form of el jefe (boss). Spanish typically marks gender on many job titles: el jefe (male), la jefa (female). Jefa is standard across Latin America and Spain. In some places (e.g., Mexico), la jefa can colloquially mean mom, but here context clearly means boss.

Why is there a la before jefa? Could I drop the article or capitalize Jefa?

Spanish normally uses the definite article with common nouns like professions: la jefa. Dropping it (Jefa firmará…) sounds like a headline or a direct address (vocative: ¡Jefa!). Job titles are not capitalized in Spanish unless they start a sentence: write la jefa, not Jefa.

Is firmará the simple future? Could I also say va a firmar or firma?

Yes, firmará is the simple future. You can also say:

va a firmar (very common, often more conversational or immediate),
firma mañana (present used for scheduled future). All three are correct here; nuance depends on style and certainty.

Does firmará ever mean “must be signing” as a guess about the present?