Learn Russian: Завтра мы сами будем клеить обои в спальне. - Tomorrow we will paste the wallpaper in the bedroom ourselves.

Сами is the plural form of the emphatic pronoun сам. It emphasizes that 'we' are doing the action on our own, without outside help. You would use the reflexive pronoun себя if the subject was also the object of the action (like 'we see ourselves'), but here the object receiving the action is the wallpaper.

Why use the imperfective future будем клеить rather than a perfective future verb?

Pasting wallpaper is a time-consuming activity. Using the imperfective future emphasizes the ongoing process of doing the work tomorrow, rather than focusing purely on the completed result.

Is обои a plural word?

Yes! Unlike English where 'wallpaper' is usually a singular or uncountable noun, the Russian word обои is always plural. Because it is an inanimate object, its accusative form (used here as the direct object) is exactly the same as its nominative form.

Why does спальня change to в спальне?

It is in the prepositional case because it answers the question 'where?' following the preposition в. For feminine nouns ending in -я, the ending changes to -е in the prepositional case.