I assume you have a vacuum head and hose already. Typically the vacuum hose hooks into the skimmer line (pump suction side) somehow. This could be a dedicated port where you hook the hose and throw a valve, or a simpler kind where the hose fits onto a device that you lay in the skimmer and then the water is sucked through the hose instead of the skimmer opening to the pool. In either case, depending on the pump type as to whether it can prime easily, you may want to submerge the hose and fill it with water before connecting it. This eliminates an air bubble that could screw up priming.
Can you elaborate on what you have and also the water pressure issue?
Hope this helps.
Al