What is longitude? what is latitude?

Longitude and latitude are used as coordinates to find places on the Earth without having to use a name. (Say, perhaps you're in the ocean and there's nothing that can be referenced)

It's similar to using x and y coordinates to locate points on a 2D plane in math, except the grid is wrapped around the Earth.

Longitude is vertical and measures how far left or right you are (from the prime meridian)
Latitude is horizontal and measures how far up or down you are (from the poles/equator)

This link explains it