As you have seen in the previous lessons, the Russian equivalent of the verb to be is not used in present tense sentences.
The verb to be does exist in Russian, but in the present tense it is used only in structures that are focused on the existence of something or someone. (You will learn those structures later in the Resonance Textbook and Study Guide.)
However, in all other structures the present tense form of the verb to be is omitted as shown in all sentences you have already came across.
Э́то актри́са? Is this an actress?
Э́то телефо́н. It is a telephone.
Э́то не кни́га. It is not a book.
If both parts of the sentence are expressed with nouns, the omitted present-tense to be is represented by a dash.
О́льга [noun] – актри́са [noun]. Olga is an actress.
Андре́й [noun] – инжене́р [noun]. Andrey is an engineer.
But no dash in other cases:
Он [pronoun] фе́рмер [noun]. He is a farmer.