The basic requirements for a pot holder are that it be large enough and thick enough to protect your hand and wrist from hot pots and pans. To make one, you need quilted fabric, thread, and 1/2 inch-wide double-fold bias tape. The bias tape is available at notion counters.
Or make your own: cut 1 1/2 inch-wide bias strips, fold under both outer edges 1/4 inch; then fold the binding in half lengthwise, with one side slightly wider than the other.
Cut an 8-inch square with rounded corners, or an 8-inch circle of quilted fabric. Begin binding at one corner of the square, anywhere on the circle. With the wider side underneath, wrap the bias around the fabric’s raw edges: topstitch through all layers. At the end, make a loop for hanging: sew through just the bias for 4 inches, cut the bias and loop the end back onto the bound edge, then stitch the end to the edge with zigzag stitches.
For a casserole pot holder, cut a strip of fabric 5 x 32 inches for the body. and 2 pieces each 5 x 8 inches for mitts. Bind one 5-inch edge of each mitt piece. With raw edges aligned, pin a mitt piece to each end of the body and round out the end corners. Starting at the center of one long edge of the body, bind all around the edge, taking care to catch all layers in the stitching. At the end, make a loop.