Determine the size of the frame. Of course the frame has to be at least the same size as the picture. If you're matting the picture, that will add to the frame size. Finally you want a frame that has a strong presence but not too big to overpower the picture. For pictures up to 8-by-10, a frame with 1 inch to 2 inch wide sides, top and bottom is a good rule of thumb. If the picture is larger, then you can have larger widths.
Cut the wood into the following lengths, two at 11 inches and two at 14 inches. This is this the size of a frame you need for a 8-by-10 print that is matted to 11-by-14 inches.
Using a miter saw or miter box, cut 45 degree angles at the end of the each length and sand the cuts so they are smooth. For added style you can use a router to create an bevel on the edge of each length that will be the inside of the frame.
Stain or paint the frame the color you want. Once dry, assemble the frame by lining up the ends and using small finishing nails to hammer together.
Place the glass and matted print on the back of the frame. Secure in place using a backing mat. And your frame is ready to be hung.