the Basics

in my experience, in order to de-Mystify the whole process of playing guitar,
so that playing becomes enjoyable and understandable,
here's what you've got to know...

the way to approach guitar is to find similarities and patterns in everything that you play.
I've been playing for a couple of decades, so i can show you what those similarities and patterns are and how they apply to the music that you want to play. here's the basics; use this as a check list for when you take lessons. you can get more in-depth info about these basics on my Piczo site as well.

• the Musical Alpahabet - like the regular alphabet, except it starts over after G, and you've got sharps (#) and flats (b) in between these notes

• where these notes are on the guitar - easy patterns to learn this - the strings are Eat A Darn Good Breakfast Everyday. the 3rd -5th-7th frets of the E and A strings are
  [E]-->G, A, B, and [A]---> C, D, E (corn Dog Extravegazna) --- from there you can use disco Octaves and other fun-sounding strategies to find the notes on the guitar, until you just know them like the back of your hand.
  

• the Major Scale - it's the backbone of all music in the western hemisphere; it's the tools you use to build a song, whether it be pop, rock, jazz, country, blues, funk, classical, wutever, and weirdly enuff, it's the same as the Minor Scale (but just starts on a different note). it's the do-re-me-fa-so-la-ti-do scale. [enjoy that link :-D]
  

i can show you 5 different ways to play this scale (and it works in every key), so that, if you memorize just 5 patterns, you can play every major and minor and many more scales all the way up and down the neck of the guitar; pretty useful for composing, solo-ing, improvising, and understanding.

• Chords - start with open chords C-A-G-E-D

learn those "open" chords as Majors, Minors, and Dominant
(in other words, learn C major, C minor, C dominant (a.k.a. C7).,
A major, A minor, A dominant, etc..etc...)
-then you can learn to "transfer" those chords using "bar" chords. if you can play C, A, G, E, and D as majors, minors, and dominants, you've got the key to playing along with virtually any song on the radio, iTunes, youTube, etc... because they are based on Harmonized Major Scales.

• Harmonized Major Scale - this is playing a Major Scale with chords

so now there are lots of other things to learn on the guitar, like arpeggios, pentatonic scales (which are just simpler versions of the major scale), how to use modes, other types of scales (the only other scale that is popular in our culture is the HarmonicMinorScale, and it will remind you of an Egyptian or Spanish style anyway.

you can get more in-depth info about these basics on my Piczo site as well.

*********
but the most important thing is to enjoy playing and to learn songs/styles that inspire you and play these songs with people and entertain other people with them.

a good teacher can patiently help you do this.

i've seen someone take a week to learn his very 1st song, and i've also seen it take close to a year for others, it depends on your understanding of music and how consistently you practice.

i recommend taking lessons once or twice per week and practicing about 15 minutes per day. if you get inspired and want to go longer, great. but as long as you are going at least 15 minutes, every day and it becomes a habit, you'll build some muscle memory and before long you'll be playing for hours at a time without even wondering where the time went.