Download the plugin Loco Translate
or program https://poedit.net/
If you translate a program, find a pot or po file in the theme folder... open it, translated into Russian and save. The output will get 2 files po & mo. Upload them to a folder. Attention. the file name plays a role. See texdomain. Should be something like en_us.po or nazvaniyami-en_us.po
The files are usually in the folder languages || lang.
PS is such that all strings are prepared for translation, or even the whole theme is not localized, then edit the code directly (though this is a bad way) or create a doch. theme and templates wrap the code in the correct PHP code for localization, create yourself a pot file and translate.