Guitar is a fretted musical instrument that usually has 6 strings but the number of strings can go up to 32 strings. It is either played with both hands either by using a pick or by using fingers/fingernails while fretting the strings with the left hand(if you are right handed). Guitar is a very popular musical instrument and is used in any genre of music like jazz, pop, metal, rock, hip-hop etc.
There are three main types of modern acoustic guitar: the classical guitar (Spanish guitar/nylon-string guitar), the steel-string acoustic guitar and the arch-top guitar, which is sometimes called a "jazz guitar". The tone of an acoustic guitar is produced by the strings' vibration, amplified by the hollow body of the guitar, which acts as a resonating chamber. The classical guitar is often played as a solo instrument using a comprehensive finger-picking technique where each string is plucked individually by the player's fingers, as opposed to being strummed. The term "finger-picking" can also refer to a specific tradition of folk, blues, bluegrass, and country guitar playing in the United States. The acoustic bass guitar is a low-pitched instrument that is one octave below a regular guitar
The picture above is a acoustic guitar which is mostly played with your finger/fingernails. It is the most widely used form of guitar and is used in most genre of music(except for metal or rock).