Notes in parenthesis

You should write in Russian here in the Russian forum. There is very active English forum here if you are comfortable with English as you seem to be. I use Google to translate, so I will answer in English anyway.

It sounds like the note will be silent so I will work on that assumption and you can ignore the muting the note if I am wrong.

Put the note in an unused voice. Select the voice by pressing ctrl+alt+# (# is 2, 3, or 4). Enter enough rests to put the entry point where you want it. In you picture you will want to enter a half rest and a quarter rest. Next enter the note you want, in your picture it will be a G (entered as 5 G and you will probably need to change it's octave by pressing ctrl+the down arrow). Select the note and look in the inspector (press F8 if needed). in the Chord section check "Stemless" and "Small." To mute the note uncheck "Play" in the note Note section. While the note is selected open the accidentals palette and double click the brackets () and they will be applied to the note. You can now delete the unneeded rests by selecting each one and pressing the delete key. If you want the note moved to the right a little as in your picture, select the note and use the Chord section of the inspector and change the "Horizontal offset" so that it looks like you want it.