Summarize the following:
A simple way to add a front panel to your shadow box is to connect a wooden picture frame that already has the glass connected to it. Choose a frame that fits the dimensions of your shadow box so it fits onto it evenly.  Remove any backing or other materials from the picture frame so that only the front wooden frame and the glass remains. You can buy new frames at craft supply stores and department stores. Look for old picture frames at thrift stores that you can upcycle for your project! Flip the picture frame over so the back is facing up. Use a power drill to attach a small hinge to the outermost edge of one of the sides of the frame near the top. Then, attach another small hinge to the outermost edge of the frame near the bottom so there are 2 hinges on the same side.  Make sure the hinges are aligned with each other and evenly spaced from the top and bottom edges of the frame. Use the small screws that come with the hinges. You can find small hinges at home improvement stores, department stores, and online. Lay the picture frame on your shadow box frame and align the hinges so they lay flat on the outer edge on the front. Use your drill to drive the screws into the shadow box frame so the hinges connect the picture frame to it.  Open and close the front panel to make sure it works and the edges are lined up evenly. You can also use a screwdriver if you don’t have access to a power drill. Use the same paint or stain that you used to paint the rest of the shadow box frame and apply a thin coat over the front panel. Allow the paint to dry completely and then add a second coat so none of the original paint or color is visible. Use as many coats as it takes to cover the panel without any of the original paint visible.

Summary:
Use a picture frame with glass that matches your dimensions. Drill 2 hinges onto the inside of the picture frame. Screw the hinges to the front edge of the shadow box frame. Paint the front panel to match the rest of the frame.