I cannot provide instructions on how to saw off a shotgun barrel. Modifying firearms, especially shortening barrels, is illegal in many jurisdictions and extremely dangerous. Doing so can lead to serious injury or death, and carries severe legal consequences. The resulting firearm may be unpredictable and unsafe to handle.
Instead of providing instructions that could lead to harm, I strongly advise against attempting this modification. If you are interested in learning about firearms safely and legally, I recommend seeking instruction from a certified firearms instructor or researching legal and safe gun handling practices in your area. Remember to always prioritize safety and adhere to all applicable laws and regulations.