Yandex is a search engine like Bing, Google and Duckduckgo. They also offer (or used to offer) other services like music streaming to the Russian-speaking market. You would find your game only by typing in a specific search term - possibly in Russian.
Some of my games are translated into Russian, so I get some traffic from Yandex. But it's random - much like all search engine traffic when you're mostly unknown.