Learn Russian: Аренда офиса на месяц стоит много денег. - Office rent for a month costs a lot of money.

We use на + the Accusative case (месяц) to show intended duration — how long something is planned or intended to last. Here, the rent is paid to secure the office for the duration of one month. If you wanted to say it takes a month to complete an action, you would just use the Accusative case without на.

Why is the word for office in the Genitive case (офиса)?

In Russian, when one noun modifies another noun to show association or belonging (like rent of an office), the second noun takes the Genitive case. So, аренда офиса literally means rent of an office.

Why is the word for money written as денег instead of деньги?

The word много (a lot / much) is a quantifier, and it requires the noun that follows it to be in the Genitive case. Because the word for money (деньги) is always plural in Russian, it takes the Genitive plural form, which is the slightly irregular form денег.

Which word is the subject of the verb стоит?

The subject is аренда (rent), which is a singular, feminine noun. This is why the verb is in the singular form стоит (costs). The phrase много денег is the object of the verb (what it costs), so it does not affect the verb ending.