Set the fence of the table saw 1/4" from the blade. Place the long side of the board firmly against the fence (and flat on the table) and run the board through the saw from the mitered edge until you reach the stop line. Then, carefully retract the board until it safely clears the blade.
Turn the saw's motor off. With the stock and your hands clear of the blade, move the fence an additional 3/8" away from the blade and make another cut, parallel to the first and again up to the stop line. To be safe, the saw should always be turned off while adjusting the fence.
Repeat the previous step until the entire width of the board is cut into fingers, about 1/4 inch wide. The finished featherboard should look like the example in the image on this page.
NOTE: If the last cut yields a very thin finger, you may wish to remove that finger altogether. If the last finger is greater than 1/4 inch in width, make one more cut. You don't want any fingers to be more than 1/4 inch in width, as that may cause the finger to be a bit inflexible and can bind the wood when the featherboard is in use.