Each of the strings in a guitar has a specific tune assigned to it. These pitches are commonly called guitar tunings and they can be pre-set by the manufacturer of the guitar or changed by the guitar players themselves. The pitches that are given to each string follow the notes that are used in Western music.
To be able to get the desired pitch or tune of the strings in a guitar, the strings would manually have to be adjusted by rotating the tuning pegs at the end of the guitar neck. Many guitarists tune their own guitars by following different manuals.
There are basically two types of guitar tunings. The first one is the standard tuning and this is the basic pitches that are readily assigned to a guitar once manufactured. It follows the pitches E, A, D, G, B and the high E. the other type of tuning is the nonstandard or alternative tuning.
These are the types of tunings that have specific variations from the standard ones. Under the alternative tunings are open, crossnote, and special tunings. Under these subcategories are hundreds of variations. These are produced by guitarists and musicians who are tuning their guitars specifically to match the song that they are playing.