The tail board is designed to withstand more pulling tension. If you look at the diagram below you'll understand why. So it depends on what you're building as to how you'll want to situate the pins and tails.
You'll need to determine the size and number of tails. For this project I'm going to use two tails. I'm also using a handy dovetail marker and a marking knife to mark the angle.
How you mark the tails will depend on the tool you're using. In my case, I'm going to use a pencil to mark 1/4 inch from each edge. Then, I'm going to find the center and mark 1/8 inch on each side of the center. This will leave 1/4 inch in the center of the board.
Next, I'm going to use the dovetail marker to mark the angles. Start with one side of the board, and use your marking knife to mark down to your depth. Then, mark four lines across the top of the board, and use the dovetail marker again to mark the other side. The picture will be much more helpful than the paragraph above.
Now we are going to cut away the wood to leave the tails. Use the dovetail saw to cut across the wood to the base of the tail on each side of the wood. Make sure to follow your mark. Do this on both sides.
Now chisel away from the front of the wood removing only small pieces of wood at a time. This process will take some time and you shouldn't try to rush it by chiseling away too much at once. Alternate back and forth between step 7 and step 8 until you've reached the center.
It's important not to chisel all the way through to the other side of the wood because you'll risk damaging the other side. So once you reach the center of the board you should flip it over and start again from the other side.
Your tail board is almost finished. You can clean up any uneven or rough edges with a file or sandpaper. You want the edges to be as straight as possible, but don't remove too much of the wood.
Using your marking knife, trace the edges of your tail board onto the end of the pin board. Using the marking knife leaves a tight, clean line—especially compared to something rough like a pencil.
You may have noticed the one side of the pin board has wider pins. You'll want to start chiseling on the side with wide pins. Because the area you're chiseling is angled, you need to be careful not to chisel into the edge of the pin. Just as you did with the tail board, remove small pieces of wood until you reach the center of the board, then flip it.
Don't worry, dovetails require practice. I'm still improving on my technique every time I make one. If the wood doesn't fit together well don't force it, but you may need to tap lightly with the mallet in order to make them fit. You may also need to examine where the wood is too tight and fix this with a file or sandpaper.