Learn Hardcore Russian: Мама пылесосит комнату перед ужином.

Пылесосить is an imperfective verb, used for ongoing or habitual actions. Its perfective counterpart is пропылесосить, which indicates the action will be viewed as complete (e.g. Мама пропылесосит комнату перед ужином means “Mom will have vacuumed the room before dinner”).

What does the -ит ending in пылесосит tell us?

The -ит suffix marks 3rd person singular present tense of an -ить verb—it tells you the subject is “he/she/it.” Here, Мама пылесосит means “Mom vacuums” or “Mom is vacuuming.”

Why is комната in the form комнату?

Because комнату is the accusative singular of комната (a feminine, 1st-declension noun). As the direct object of a transitive verb, it takes the accusative case; inanimate feminine nouns end in -у there.

What case is ужином in, and why?

Ужином is the instrumental singular of ужин (masculine, 2nd-declension). The preposition перед, when used in a temporal sense (“before”), requires the instrumental case.

What's the difference between перед ужином and до ужина?

Both mean “before dinner.” Перед ужином often implies “immediately before dinner,” while до ужина can refer to any time beforehand. In everyday speech they’re largely interchangeable.

Can I change the word order? For example: Перед ужином мама пылесосит комнату?

Yes. Russian word order is flexible. Placing перед ужином at the beginning emphasizes the time without altering the basic meaning.

How do I say “Mom is vacuuming the room right now”?

Russian uses the same present tense for both general and ongoing actions. To stress “right now,” add an adverb like прямо сейчас:
Мама пылесосит комнату прямо сейчас.

Where is the stress in пылесосит, and how do I pronounce ы?

The stress is on the second о: пылесОсит [pɨlʲɪˈsosʲɪt]. The ы is a central unrounded vowel [ɨ], produced with the tongue slightly lower than for и [i].

How is пылесосить formed morphologically?

It comes from the noun пылесос (“vacuum cleaner,” literally “dust-sucker”), itself from пыль (“dust”) + root of сосать (“to suck”), plus the infinitive ending -ить.