That's a really nice looking tool - very easy to use. I bias the VH4 by measuring current with a multimeter at the output transformer, but you have to be careful using that method because you can get a painful shock if the probes touch.
Using the tool you linked to, I would use this step-by-step method.
1. Unplug everything from the amp.
2. Remove the 4 screws on the bottom of the amp (not the rubber feet screws - the other 4 screws).
3. Remove the 6 screws on the rear of the amp that hold the metal cover on. Remove and set aside the metal cover.
5. Place the amp upright facing away from you (controls facing away from you).
6. Place 2 stacks of books on top of a table (or on top of the amp's wooden chassis). The book stacks should be high enough to clear the height of the power tubes plus the height of the bias tool's plugs. The stacks should be spaced apart from each other equal to the distance between the 2 transformer blocks on the amp.
7. Remove the metal amp from the wooden chassis by sliding it backwards. You may need to lift it a millimeter or so at the rear as you first slide it backwards to clear some of the tape inside the bottom of the chassis. Place the amp upside-down on the 2 stacks of books so that only the 2 transformer blocks are resting on the books. Be sure the components in the middle (tubes, capacitors) are not touching the books or the surface below. The amp controls should be facing you, with the speaker/power connector at the rear of the amp.
8. Plug in your bias tool plugs and new power tubes. Confirm that the tube selector switch (if your VH4 has one) is set to EL34 for EL34 tubes. The switch is next to the tube plugs on the same surface of the amp that the tubes plug into.
9. Connect your speaker cabinet to the correct output connector (4, 8, or 16 Ohm).
10. Connect power.
11. Turn the amp power on. Wait 30 seconds, turn standby on.
12. Your bias tool will measure the current through each individual tube. For EL34s you'd want each tube to read between 30-35mA. If it is reading too low for all tubes you will need to adjust the bias trimpot higher (clockwise). If it is reading too low you will need to adjust the bias trimpot lower (counter-clockwise). If your amp is oriented as outlined above the bias trimpot will be located toward the left side of the circuit board. The trimpot all the way to the right of the circuit board in front of the output transformer is the hum trimpot. To make adjustments to the bias trimpot use a small insulated flat-head screwdriver. Make small adjustments and watch the change in the reading. To prevent from getting shocked I always turn power/standby off while adjusting the bias trimpot, and then back on to take a current reading after making the adjustment.
13. After confirming the bias is set correctly, go in reverse order! Remove the bias tool plugs and put the new tubes back in their socket (after they have cooled down a bit). Place the amp back inside the wooden chassis. Tilt it forward and screw in the 4 bottom screws. Attach the metal plate with the 6 screws, and you're done!
Others can chime in on the best bias reading. I'd shoot for 33mA as a starting point.
As a note of interest the difference when measuring at the output transformer is that a pair of tubes is measured at a time instead of each individual tube. So instead of looking for 30-35mA, you'd be looking for 60-70mA (2x the reading for a pair).
