For beginners we highly recommend reviewing the User Manual, there are step by step guides to show you how to plug instruments and what all the knobs do. There's another section on installing Studio One and getting up and running to monitor your instrument as you are asking.
The user manual can be found in the download section in your my.presonus.com account or on the product page.
Here is a link to the AudioBox 96 manual for you.
Here's a video that walks you through this as well: