Larisa, thank you)
MasteR, I can't find the reply function in a private message; I saw the set, and I'll take a closer look in a couple of hours and ask all the questions I have there.
When you open someone's message, click the "quote" button, and write your message. Then send it.
Alternatively, go to the profile of the person you want to write to; there's a line that says something like "send a private message."
