Again to keep things more simple, the Meridians are usually referred as being from 180 degrees West, to Greenwich, then to 180 degrees East. 180 East, just East of New Zealand, and this is called 'the date line', to be explained later. On a globe they appear as bands that all meet each other at the North and South Poles. They are not parallels. They actually all touch each other at the North and South Poles on a globe.
Longitude measures how far east or west along the equator something is.