Yandex.Browser has identified useful and safe extensions and selected the most popular ones. You can find them on the extensions page (to get to this page, click → Extensions).
You can also install extensions from the Opera Catalog. All extensions from this Catalog are compatible with Yandex.Browser. To do this:
After installation, the extension appears on the extensions page. To enable it, click the On button to the right of it.
More information can be found in the Extensions section.