Copper can combine with many different elements to form many different minerals. Mostly though, the ore deep in the ground combines with sulfides and near the surface it reacts with oxygen and water to form several kinds of beautiful blue or green minerals. Copper ore is usually present in its oxide mineral forms near the surface as that is where it will be most exposed to the atmospheric oxygen and water. In a well-funded exploration, geologists can study the geological history of the area, and determine the processes that occured in certain locations that were likely to bring about concentrated deposits. Either that, or explorers get lucky, and find it by a lot of digging and hard work.
Companies often employ more technologies in locating ore deposits.
They can drill deep into the ground, and obtain samples a mile beneath the surface. They also have instruments that can detect gravitational variations in certain areas that indicate changes in material density beneath the surface. Sometimes the magnetic properties of metals can be exploited to find them under the ground as well. Since there are two major different types of ore, each has unique methods of processing and extraction. Well, if it is parallel with the surface, you will usually want to use an open pit mine.