The best place to start for a fork is the manufacturer's website. Type the manufacturer, model name, and year into your favorite search engine, and you should be able to find help, including recommended settings, service intervals, and more. Some manufacturers like Fox and RockShox also offer an app to help you set up your suspension without leaving your garage.
You can find recommended air pressure values for your bike's rear shock on that model's product page on our website or at www.marinbikes.com/support. Just weigh yourself (preferably in your riding kit), find your bike model, and set your shock to the indicated pressure. Note that proper sag settings are paramount to ensuring a proper ride. You can find air charts for our various full suspension models on our Support Resources page.
If your fork or shock isn't listed on a manufacturer's website, the next port of call should be your local Marin dealer.