Your sandbox site is a testing environment where you can try out different settings, create new grading scales, etc. without affecting any of your real data. You can get to it by putting ".sandbox" in the middle of your school's normal URL: https://yourschoolname.sandbox.schoolrunner.org.
The sandbox a completely separate copy of your database, so any changes you make will not affect data on your production (regular) site. Sandbox sites are not updated in real time though, meaning that data entered in your production site does not immediately appear in your sandbox site. If you notice that information is too out-of-date in your sandbox site, contact your Schoolrunner administrator to have the latest production data copied to your sandbox.
If you are practicing or experimenting in Schoolrunner, be sure that "sandbox" appears after your school name in the URL to ensure you're not making changes to your production site. To further distinguish sandbox sites from production sites, there is a dashed yellow border around the window in sandbox sites:
Log into your sandbox site with the same user name and password that you use on your production site. (If your credentials don't work, your account may have been created after the last production-to-sandbox copy was made, meaning your account didn't exist yet and thus not copied over! Contact your Schoolrunner administrator to rectify this.)