Purchase a good guitar. Visit a music store that sells used instruments. Let the store manager help you pick out one that is within your budget, that fits your body, and will keep a tune. You should be able to sit comfortably on a stool and fit one arm over the body of the guitar, easily reach the end of the fret-board with your left hand, and be able to span the width of the keyboard with one finger. Decide whether you want nylon strings or metal on your guitar. Nylon strings are easier on your fingers, but metal strings will hold their tune longer.
Tuning is the term for turning the tuning pegs on the guitar to stretch the strings till each is at a specific pitch. The standard tuning for a guitar, starting from the base string is E, A, D, G, B and E. These are the notes each string should make when picked without holding it down anywhere along it, or in musical terms, when it is open.
You can use an online guitar tuner if you have a computer, purchase a recording, a pitch pipe made for guitars, or an electronic tuner to help you get each string to the correct pitch. Be careful not to make the strings too tight. This is called "over-tuning," and can cause broken strings or even damage to the neck of your guitar.
Chords are made by placing the tips of your fingers between specific frets --- the little bars that go across the guitar neck --- on specific strings. The most common chords are C, G and D. Once you learn these three chords you can strum at least 80 percent of most common folk songs. Purchase a beginning book on strumming, take advantage of free online guitar lessons, or sign up for music lessons.
To play a melody on the guitar, you will need to learn how to play individual notes. This is done by holding down one string by placing a fingertip between the frets, and then picking that string. For example, if you place your finger between the second and third frets, counting from the neck of the guitar that is a F. It is a good idea to learn how to read notes as you learn how to play them on your guitar. As with chords, there are free online lessons, books and people willing to give lessons.
After you have learned how to make more chords than the basic C, D and G --- and you have learned how to pick a simple melody --- you will want to learn some fancier ways to play your guitar. One of the easiest is hammer on and hammer off. Hammer on is a technique where you pluck the string then put your finger down on it, changing the note. Hammer off is where you are holding the note, pluck the string and then pick up your finger. Power chords are two string chords that are played in succession, often used as part of the rhythm section of a song. Vibrato is created by moving your finger while it is on the string. Oddly the real action for this technique is generated by elbow movement.