Learn Farsi: همیشه باید هر دو دست را روی فرمان گذاشت. - One must always put both hands on the steering wheel.

This sentence uses an impersonal structure to give a general rule, meaning 'one must' do something. To build this, we use the invariant word باید followed by the short infinitive of the action verb. The short infinitive is identical to the past stem, which is why we use گذاشت (to put) without conjugating it for any specific person.

Why is دست (hand) in the singular form when the translation says 'both hands'?

In Farsi, nouns that come after numbers are always kept in their singular form. Since هر دو means 'both' (literally 'every two'), the noun that follows it remains singular as هر دو دست.

Why do we need the word را after the hands?

The word را is the specific direct object marker. Because the sentence refers to a specific set of hands (both of them), هر دو دست is a definite object. We must follow it with را to clearly show what is being put on the steering wheel.

I learned that فرمان means 'command'. Why is it translated as 'steering wheel' here?

The word فرمان is actually used for both a 'command' and a car's 'steering wheel' in Farsi. Since this sentence talks about putting both hands on something, the context tells us it refers to the steering wheel!