Press the key which sounds like the Russian letter you want to type. For example, to type д, press D. This keyboard follows the AATSEEL “phonetic” Russian keyboard layout.
Some characters need a shortcut with Alt, e.g. to type =, press Alt + = or Alt + 0.
If your keyboard layout is not US/UK English, you may have to use alternative keyboard shortcuts for some letters, e.g. Alt + U for ю. Stop the mouse over each button to learn its keyboard shortcut(s).
You can select text and press Ctrl + C to copy it to your document. In your target document, press Ctrl + V, or, if you want to paste the text without formatting, try Ctrl + Shift + V. Press Alt + Enter to turn the Russian layout on and off.