Questions & Answers about Я не могу клеить обои сам, но могу чинить мебель.
Why do we use сам here instead of себя or один?
The word сам emphasizes that the subject (я) is doing the action personally, without help. Себя is a reflexive pronoun meaning 'oneself' as a direct object (like 'I see myself'), and один means 'alone' or 'by oneself' in a physical sense. Here, 'I cannot paste wallpaper myself' means 'I cannot do it without assistance', which perfectly matches сам.
Does сам change if a woman is speaking?
Yes. Сам is the masculine singular form, so we know a man is speaking in this sentence. If a woman were speaking, she would say сама. This emphatic pronoun always agrees in gender, number, and case with the noun or pronoun it refers to.
Why is the word for wallpaper, обои, in the plural?
In Russian, обои is a plural-only noun, much like 'scissors' or 'pants' in English. Even if you are talking about the wallpaper for a single small wall, you must use the plural form. It is in the accusative case here because it is the direct object of клеить, and for inanimate plural nouns, the accusative looks exactly like the nominative.
Why are the verbs клеить and чинить in the imperfective aspect?