The key item to look at is your mash tun. If you open your equipment profiles and click on 'Equipment Wizard', the program will walk you through the key pieces of information to get you started. You will need to know your boil off rate, trub loss, and approximate brew house efficiency or be able to give it a good guess to get yourself started. Once you have brewed a batch or three, you can look at the process and determine just what your boil off rate was (pre-boil vs post boil volumes), grain absorption rate (total volume of water into the mash tun vs pre-boil volume), loss to trub, and brew house efficiency (BeerSmith will give you an actual calculation of this on the 'session' tab of your recipe if you fill out all the gravity and volume measurements.).
There are also a few YouTube videos on setting up an equipment profile in BeerSmith which you can search for. Even if they are a bit dated, the essential process is the same.
