Just open the valve on the pump.
The zero loss connector screws onto the valve on the suspension with the t bar fully anticlockwise. It is nipped up, not mauled, with a 17 mm spanner. There will be air in the hose so before nipping up, close the brass tap on the pump and fill the reservoir, then pump it a few times to expel the air first. Once it is connected, tighten the t bar on the connector and the system pressure will register on the gauge. Undo the brass tap to let fluid out and tighten to pump it in. Old hands will suggest that once you gave pumped it up to about 300, you should release all the pressure and pump it to the correct height. Then give the car a good scragging before leaving it for two hours and adjusting the ride height to taste and level both sides.