What brand is it? You can oftentimes google the brand and "manual" and find a manual for your particular pressure cooker. Different ones operate in different ways. For example, does yours have a pressure guage or just the weight?
Mary Beth is right. Look on-line my pressure cooker had the manual available and other great info. They are great to use for quick meals. Still getting the hang of it. My sister started using hers and her boys wanted seconds then thirds of some stew. (Bless her heart - she never really got into cooking but she can now make a great stew!! ) Good luck, Barbara
Fannie, you can write to the company that made the pressure cooker and I am sure if you include the model and maybe the serial no. they will sell you a book with lots of helpful information in it.
Just found a wonderful site for pressure cooker and canner parts. I was needing a gasket for my 6qt Presto cooker. It's on its way! :-) There are manuals for many of the pressure cookers and canners too. http://www.cookingandcanning.net/