First, print out the image above. Use a copy machine with resizing capabilities to either enlarge or shrink the image, depending on the size of your wooden disc. Once you have it the size you want, place it on top of the wooden disc.
Using a pencil, trace over the outline of the pattern, pressing down so that you make an indentation in the wood. Once the design is indented, use the pencil to go back over the indents, making a complete pencilled pattern on the wood.
If you're painting, use your paints to go over the pencil lines. If you're using a woodburning pen, carefully trace over the lines -- depending on how experienced you are with woodburning, it may take a couple of hours.
When you're done, brush a few coats of polyeurethane over the design to give it some shine and to protect it from wear. If you like, use a small drill bit to make a hole in the center for incense sticks. Finally, if you're concerned that your pent might scratch your altar top, cut out a circle of felt the same size as the wooden disc, and glue it to the bottom of the wood.
Use your pentacle on your altar to consecrate ritual items, to bless or charge talismans, or to represent the element of Earth. Alternately, you could attach a hook to the back and hang it on your wall.