Congratulations! You are starting on an incredibly rewarding journey as a musician and an individual. Music is a healthy brain exercise, social connection, and stress reliever. Whether this is your first instrument or your tenth, guitar is a wonderful way to stretch your abilities and expand your horizons.
The guitar has its origins in stringed instruments over 4,000 years ago. It owes most of its heritage to music evolution in Spain, but today's guitar in also related to the lute in Europe. You can hear its voice today in country, folk, and indie music as well as the electric version in rock. It is a beautiful and versatile instrument with roots almost as old as music itself, enjoy your journey!
First things first, you need something to play! Start out with a borrowed instrument or a cheap instrument. Perfecting your technique on a lower budget item is more important than getting the perfect instrument. However, you should not go with the first guitar you encounter. There are two main items you should consider in selecting a first guitar. The "action" or the distance of the strings from the neck of the guitar should not be too large. You can test this by pressing down the strings with your left hand as though you were trying to shape a chord. If it hurts on the first try, the distance is too large. The smaller this distance, the easier it will be for you to sustain practice time and switch between chords. Second, make sure your guitar can be tuned. Ask the person from whom you are buying or borrowing how often they have to tune their instrument while playing.
Lay your guitar on your lap with the larger part to your right and the narrow part, or the neck, to your left. The string nearest you is low E, and the string farthest from you is high E. From skinniest to thickest, your guitar strings are EBGDAE. You can remember this by, "Every Body's Guitar Dances All Evening." Your right hand will strum the strings over the hole in the body of the guitar, and your left will push down combinations of strings. Notice the lines in the neck of the guitar. Each of these lines markes the boundary between frets. Pushing down a string in the first fret increases the pitch by a half step. Each time you move your finger down past another line you will increase the pitch by another half step.
To find a tuner, simply google guitar tuner or obtain a tuner app. I recommend Guitar Tuna or Practice+. Tune one string at a time. If you have a trained ear, you can tune the guitar to itself by using the above knowledge of the frets to bring the pitch of a lower string to the pitch of a higher string, listening to the conflict between the two, and adjusting the string that is not being adjusted by the finger on the fret. For those of us with average ears, lay the tuner on or near your guitar and watch the needle on the tuner as you strum your desired string. Adjust your string using the pegs at the head of the neck and try to bring the needle as close to the center of the screen as possible.
Important note: if your lower strings are flat, you should turn the pegs away from the guitar, but if the top three are flat, you should turn the pegs toward the guitar. The two halves work differently.
You will be more likely to practice if you have a song you enjoy to work on. Choose a song that means something to you that has a fairly simple chord structure. This means you want a song with a few chords repeated in the same order throughout the piece. You may want to consider something by Taylor Swift, many pop songs, or if you are religious, popular worship songs played in contemporary Christian culture. "Love Story" by Taylor Swift, "Revelation Song" by Kari Jobe, or "Be Thou My Vision" are all examples of simple chord progressions. If you do not like any of these genres, pick a repetitive song that you are familiar with and look up the chords in the song.
Use the Internet!
These websites will be your greatest teachers, especially Youtube. Start by looking up the chords in your chosen song on Ultimate-Guitar.com or 911tabs. Once you have found this, use a guitar chord sheet such as this one, and match your fingers on the neck of the guitar to the shape of the black dots on the picture of the chord on the sheet. Search youtube for tutorials about guitar and about your specific song.
Once you know which chords are in your song, practice making the required shape on the strings with your left hand, then releasing your hand, then finding the shape again. Do this over and over until you are comfortable with the chord. Then try to do it without looking. Repeat again until you can confidently find the chord without looking. Do this for each new chord you learn. Once you've learned your chord shapes, practice going back and forth between your chords quickly as before. Then do it without looking as before. This exercise may feel like pushups for your brain, but it will make playing much easier.
Practice, practice, practice. Schedule a regular time in your day to practice. You will not improve if you do not practice. Since you have chosen a song you enjoy, each repetition of your song that sounds more like it should will be incredibly rewarding for you. Sing along with your strumming, and enjoy the process. You do not have to, nor will you, become a professional in a day or a week.
Your fingers hurt, you're frustrated, and you feel like you will Never get this right. Stand up, take a breath, walk around, reset, and come back. You will improve. Your fingers will hurt, but do not let that deter you. Callouses will form with time, and the strength of your fingers will grow. If you need to take a break from this song, start learning a different one and come back to this one.
Pro-tip: Do not strum all of the strings every single time you strum. Save that kind of energy for the downbeats and notes you need to emphasize.
It's practice day 472 and you have finally mastered your song! And since you like a lot of other songs with similar chords you have learned them as well! Woohoo! Go you!
Now choose a song that requires you to learn chords you do not already know. Start practicing finger picking instead of only strumming. Learn more complex strumming rhythms. There are so many things you can learn, do not stop only ankle deep into this instrument.
Now that you are practically a professional, you want to play for all your friends and family and strangers. Resist the urge to play a love song every time a member of the opposite sex passes by, try not to bring it to every single possible event, and do not praise your own talent. Enjoy providing an ambiance at the park, background music at a bonfire, bringing joy to your local nursing home, relaxing at home, showing off for your mother, or impressing your significant other. Congratulations, you have mastered guitar.