You connect the low hose to the low port,( blue ), the high hose to the high port (red).
close both valves.
Use the below chart to see what you got.
If you need to add, use the yellow hose to the can and open the low side valve to allow additional R134 to enter.

​​​​​​​R-134a System Pressure Chart - AC Pro<?php/* bloginfo('name'); */?>