Questions & Answers about Мой друг кивает и улыбается.
Because друг is a masculine singular noun, and мой has to agree with it.
- мой = masculine singular
- моя = feminine singular
- моё = neuter singular
- мои = plural
So:
- мой друг = my friend (male friend, one person)
It is in the nominative case, because it is the subject of the sentence — the person doing the actions.
Here, друг is the one who nods and smiles, so nominative is the expected case.
Because the subject is third person singular: мой друг = he / my friend.
So the verbs are in the present tense, 3rd person singular:
- кивать → кивает
- улыбаться → улыбается
Russian does not need a separate word like English is here. The verb form itself already tells you the tense and person.