Learn Portuguese (Portugal): Sabes fazer o jantar? — Sei. - Do you know how to make dinner?

In English, we say "know how to do" something. In Portuguese, you just use the verb saber (to know) followed directly by the action verb in its dictionary form. So, sabes fazer literally means "you know to make", which we understand as "you know how to make".

Why is the answer Sei instead of Sim?

In Portuguese, the most natural way to answer a "yes" or "no" question is to repeat the verb used in the question. The question asks Sabes...? (Do you know...?), so the correct "yes" answer is Sei (I know). You can add sim for emphasis, like Sei, sim, but just Sei is perfectly complete!

Why is there an o before jantar?

While in English we just say "make dinner", Portuguese often requires the definite article o (the) before the names of meals. You are literally saying "make the dinner" (fazer o jantar).

Are sabes and sei from the same verb?

Yes, they are both present tense forms of the highly irregular verb saber (to know). Sabes is the informal "you" form, and sei is the "I" form.