2D Horizontal Fit is a free asset on Unity, essential and perfect for beginners for the 2D projects. It is a must have that saves your time . You keep your horizontal screen ratio same for different screen sizes. In this way, you make sure to keep your important content towards the centre of the screen. It is simple and easy to setup. Moreover, 2D Horizontal fit works with Unity 2017.1 and +. Have a look at the video tutorial from the author for more details.
Get the tool here.
Select your main camera.
Add CameraSizeHandler script to the Camera via Inspector Panel.
Press Set Projection Size Button.
Watch the demo tutorial below or on youtube.