Hello im aware of what a compression test is but what exactly is involved in a leakdown test? what tools are required and how do you do it exactly? thanks.

A leakdown test is used to measure how well the cylinders can hold pressure, it checks the sealing integrity of the valves and rings.
The tester consists of an adapter that screws into the spark plug hole, like a compression tester, and is pressurized with shop air. The cylinder being tested is set at TDC so the valves are closed. The initial pressure is noted, and then observed over time to see if it holds steady or "leaks down". A certain amount of leakdown can be considered normal, say 5-10%, above that indicates a problem. It's also significant how quickly or slowly the leakdown occurs.
By listening for the sound of escaping air it is possible to tell where the leak is. A leaky exhaust valve will be heard through the tailpipe, an intake valve through the intake, and rings through the crankcase (via the oil filler or dipstick tube).