Although there are only two main categories of guitar, within each category there is a vast range if different styles, models and varieties to ensure that there is a guitar and a sound for every occasion and performance style. The two main categories are, of course, acoustic and electrical, but to define a guitar as either acoustic or electric is very bland, and tells us nothing about the actual type, the sound it produces, or its ease of performance.
Acoustic guitars are the ones most often used as a starting point for those new to learning the guitar as an instrument, and of the types of acoustic guitar available, the one most often used and recommended as the best one for beginners is the nylon string classical guitar. The strings of acoustic guitars can be made from either nylon or string, but since nylon tends to be much kinder on the fingers than steel, being thicker and looser, this is preferable. Not only that, but compared to steel strung guitars, nylon is far easier for a beginner to use to achieve a decent quality of sound. If these advantages weren't enough for a beginner, nylon strung classical guitars also tend to have wider necks than steel strung guitars, and this means that it is generally easier to get the fingers into position over the strings for the correct chords, without so much risk of fumbling, and accidentally catching the wrong string, or more than one string, resulting in buzzing and bad chord sounds.
With all of the advantages of nylon strung guitars, it might be wondered what would possess someone to use a steel strung guitar, but of course the difference is the sound produced. Steel strung guitars produce a much louder sound, and more jangly, but the steel pushing against your fingers can be quite painful, especially in the first few weeks of learning. After a few weeks, the skin on the fingers becomes more worn, and thicker, and able to cope with the instrument, but until that time, it is a painful instrument to start to play.
Although most guitars have six strings, there are some which have twelve, and these are divided into two sets of pairs, with the normal six strings each paired with a thinner string that plays the same note, but an octave higher. This provides a very attractive sound, but as a result of having so many strings, is very challenging to play, and not recommended for beginners.
Another breed of acoustic guitars are known as resonators, and these are purely steel strung guitars, the difference being that built in to the body of the guitar is a speaker-like resonator that was originally introduced to simply add volume to the instrument, although today they are usually played by country or blues musicians, in conjunction with a slide, as they produce quite a distinctive sound.
Electric guitars are instantly recognisable, although they can be split into two main types - those with hollow bodies, and those with solid ones. Those electric guitars with hollow bodies include an acoustic sound, with the notes being mellowed or softened slightly by the fact that the notes being played are amplified naturally to some extent. As a result of this, hollow body electric guitars are preferred by those who play jazz. On the other hand, solid body guitars, which rely on electronics and external gadgets to achieve the sound, are preferred by those who play rock. Because there is no natural acoustic sound, the instrument is entirely reliant upon the electronics, but this in turn provides far greater versatility and, perhaps more importantly, greater volume!