To practice using NPSP, it is best to set up a Trailhead Playground with the Nonprofit Success Pack installed. See the tutorial and instructions below.
(This video was made for beginners originally, so some information may seem obvious to those with more experience 😉)
Sign up or log in by clicking on the buttons on the upper right corner. Follow the instructions written in the Trailhead modules or follow along with the video to complete the project.