Here is one way to cut the groove for a sliding dovetail.
Mark the depth of cut with a marking gauge on both edges of the board. Lay the dovetail piece on top of your work surface and trace the bottom of both sides of the dovetail. Transfer that line to your depth of cut line on both edges.
Now you can see where to position the dovetail on the edge of the board so you can trace its angle. Trace this angle on both edges. Connect these lines across the face of the board and this shows you where to start cutting.
The dovetail plane I used cuts a 16º angle. Bevel a 2x4 at this angle to use as a fence to guide your saw. I keep finger pressure on the sawblade so it stays tight against the fence. Saw down to your depth of cut mark and chisel out the waste between the saw marks. Slide the dovetail into the groove....and you're done!
Because the sliding dovetails on the sawbuck table are so long (25"), I'm not comfortable with this technique, so I'll show another way to cut sliding dovetails in a future post.