Simply click your mouse in the box on the left and start typing Русский according to the sounds of the letters (phonetically).

To use the words you have typed (in an email for instance), first highlight the text, then choose Copy from the Edit menu, switch to your email program, and choose Paste from it's Edit menu (help on copying and pasting).

Please note that this is not a translator. It allows you to type in Russian using a phonetic keyboard where keys are roughly matched to sounds.