Buying your guitar
Anatomy of a guitar
Tuning your guitar
Restringing a guitar
Guitars for Beginners
There are two main types of acoustic guitar: Nylon String and Steel String. Steel string guitars came later and are bigger and more strongly built as the tension on steel strings is greater than nylon. They are also a bit more difficult to play for that same reason. The 'action', which is term used to describe the distance between the strings and the fingerboard, can be adjusted at the saddle. Steel string guitars also have a metal 'truss rod' inside the neck that can be tightened or loosened to adjust the curve of the neck to fine tune the action.
You can also adjust the action and exact length of individual strings at the Bridge on most electric guitars. Adjusting the length of the strings will ensure that the 'intonation' of your instrument is correct. Perfect intonation means that no matter what fretted note you play, it will be in tune. Many factors come into it: string length, action, the degree of stretch that occurs when you press the string down, gauge of strings. An instrument with poor intonation may sound in tune in one area of the neck, but not in others, so making sure it's right is critical.
Unless you have bought the cheapest, most poorly made guitar, everything is fixable and adjustable, but take it to an expert.