Can you show me how will look robots.txt when I block only yandex bot, allow Google bot and block Yandex bot.
There are many "Yandex bots". If you want to block all the Yandex bots then:
User-agent: Yandex Disallow: /
However, if you only want to block the main indexing "YandexBot" then:
User-agent: YandexBot Disallow: /
You don't need to do anything for Googlebot (or any other bot) if you want the other bots to crawl your site, since allow (crawling) is the default action.