Any musical instrument takes many hours of practice an dedication to play well, but the guitar can be a particularly difficult instrument to get started with.
Unlike instruments like the piano which simply require pressing a key to obtain a good sound, the guitar requires that the tips of the fingers are curled and pressed down on either a metal or nylon string in the correct position on the guitar fingerboard to obtain a good sound. You also have to take into account that when you first start playing the finger tips are soft and pressing on the string can make them very sore for a while.
It takes a certain number of hours of practice but eventually the finger tips develop calluses which the idea of may not sound that appealing, but the harder surface of the callus makes it much easier to press the string and the finger tips cease to hurt after a while of playing and practicing. I frequently need to show students that it is not necessary to press hard on a string to obtain a good sound. It has more to do with good finger placement. Pressing too hard on a string can develop into the bad habit of adding unnecessary tension into the hands and arms that will impede progress in learning to play the instrument well. The left hand fingernails should be kept as short as possible in order to obtain good contact while pressing the string to the guitar fingerboard.
The guitar also requires many different left hand finger positions. We start off playing single notes on single strings and then progress to using up to 4 fingers in various configurations to play chords that can include up to 6 strings if a finger is barred across more than one string. This can require contorting the fingers into various unnatural positions that are very difficult at first. I have through many years of teaching developed exercises that help people proceed in a very gradient manner to make learning these techniques as easy as possible.
The right hand initially requires us to either learn to hold a pick correctly to strum more than one string or use it to play single strings accurately. There is also a right hand technique that requires us to pick with multiple fingers on more than one string at a time. Which ever technique is used it is essential that proper technique is learned so as to make the path to playing well easiest.
In addition to using the right and left hands correctly is is also essential to hold the instrument properly and keep all parts of the body as relaxed as possible. A guitar strap can be used standing or sitting or the guitar can be rested on the right or left knees. No way is more correct that the other, it just depends on what way you find the most comfortable and helps keep you relaxed while you play and practice.
If you are interested in learning the proper way to get started learning guitar and would like to take private lessons for the fastest progress.