Open the Minecraft Launcher, select the newly created Forge 1.8.9 profile, and click "Play." Security and Safe Downloading Practices

Using any hacked client carries significant risks.

Breaking down the file name reveals exactly what the file is intended to do:

At its core, the file Raven-BS-Client-1.8.9.jar is a Java archive file representing a modified Minecraft client, commonly known as "Raven BS" or "Raven bS". It is specifically designed for Minecraft version 1.8.9, a highly popular iteration of the game favored for its responsive PvP (Player vs. Player) mechanics. As a .jar file, it is intended to be placed directly into a Minecraft installation's mods folder, often requiring Minecraft Forge to function properly.