To check vor vacuum leaks if you don't have a vac gauge, you go around the engine bay and spray carb cleaner on the various vac hoses. If at any point the engine speed increases(revs up) when you spray carb cleaner on a certain vac hose, then there's probably a leak there.

The MAP, or manifold absolute pressure sensor reads the vacuum pressure of the intake manifold and sends that signal to the ECM. The ECM uses the MAP signal, along with other variable to determine the fuel curve the engine runs on. If you go from idle with the throttle closed, to full accelleration with the throttle open, the MAP goes from about 22in of Hg to 0. The ECM uses the changing MAP signal, along with the TPS signal and other sensor readouts to supply fuel under varying engine load conditions.

As for the timing light, it should be connected to sparkplug wire of the #1 cylinder. Just go to the plug that's closest to the driver side and trace the wire back.