Make sure you have standalone Git installed first. Reboot after installation.
In Unity, open "Window" -> "Package Manager".
Click the "+" sign at the top left corner -> "Add package from git URL..."
Paste this: https://github.com/forcepusher/com.bananaparty.yandexmetrica.git#2.0.1
To update the package, simply add it again while using a different version tag.
See minimum required Unity version in the package.json file.
Find "Samples" in the package window and click the "Import" button. Use it as a guide.
Samples also contain WebGL Template required for Yandex Metrica to work.
Drag and drop WebGLTemplates folder into Assets and select it in Edit -> Project Settings -> Player -> Resolution and Presentation. Select the template and insert your Yandex Mertica counter id found in the dashboard URL page, such as https://metrica.yandex.com/dashboard?group=day&period=month&id=89587935 where last numbers is the counter id you're looking for.
Also see the Development Repo if you want to modify this package.