If the board you're using is simply too wide or warped for your use you can rip it (cut down the length) using the band saw.
When making a rough rip cut on the band saw its often more useful and accurate to draw a line through the center of your board and eyeball the cut instead of using the rip fence.
Make sure to feed the wood through the bandsaw with your fingers and hands at a safe distance from the blade.
While most ripping will be done on a table saw, the band saw is also useful for making imprecise rips. On our big bandsaw there is a brake seen here that is used to get the blade stopped after use.