The plugin you linked is not a plugin, its a modulescript.
To use it, you have to require the module:
local CameraShaker = require(LocationOfYourModule)
once you’ve required it, you can use it to call certain functions. The devforum post already gives you tips and an example on how to use it.
Example code taken from post:
-- If you're wondering, CameraShaker is the module ^^
local camShake = CameraShaker.new(Enum.RenderPriority.Camera.Value, function(shakeCf)
camera.CFrame = camera.CFrame * shakeCf
end) -- makes shake
camShake:Start() -- starts shake
-- Explosion shake:
camShake:Shake(CameraShaker.Presets.Explosion) -- sets type of shake