Lesson 1 - first steps
As you can notice, a common guitar has six strings and a lot of frets (metal strips). Each string is tuned to a specific tone. The thickest string is the most often tuned as E (so-called low E). A little bit thinner string is tuned as A. Then there is D, G, B and the thinnest string is again tuned as E (high E). You should remember this! So again, tones (as well as names) of open strings are from the thickest string: E-A-D-G-B-E.
Now play the thickest (low E) and then the thinnest (high E) string. They sound similar, right? It is because of the same tuned tone (E) but there is an interval of 2 octaves between them. And that's why high E sounds higher than the low E.
But you can ask: "If the interval between the thickest and the thinnest string is 2 octaves, where is an octave between them?" Press the string D on the second fret (it means right before the second metal strip) with your left hand and play it with the right hand. Hey it's again tone E, but sounds higher than the low E and also lower than the high E. We found the missing octave! Now you begin to understand what means word octave.
Are you hungry for information? Read this:
In a technical language octave up means tone frequency multiplied by two. So low E has frequency 82.407Hz, E on the second fret of string D (one octave up) has freq. 164.814Hz (2x low E) and the freq. of high E is 329.628Hz (4x low E) and so on…
Exercises for this lesson:
At first, play string by string starting from the low E to high E and back. While say aloud names of these strings (E-A-D-G-B-E...). Then play random string and say aloud the name.