BeerSmith software relies heavily on your inputs for various calculations. The more accurate your inputs are, the more accurate the volumes, temperatures, color, gravity, IBUs, etc. will be. One of the first things you need to do is create an equipment profile that matches your system. Here's a link to a great video that will walk you through the process:
https://brulosophy.com/2014/08/04/beersmith-tutorial-equipment-profile-setup/
You can also edit and/or create new mash, fermentation and carbonation profiles to match your preferences.
For lots of information on various related subjects, visit:
https://beersmith.com/video/