Offcourse learning the fretboard and how octave works is the first step.
This is very well explained in the 1st series of guitar fundementals videos here, if I remember correctly.
Then you learn how chords are build. That is also explained here but what I did is also get me a book on chords theory on the side so I dont always have the face glued on the computer screen :P

Quick example of how a chord is build.

A basic chord triad is build with the 1st the 3rd and the 5th of an octave.
So if you want to play a C, the c octave would be

(1st - C, Flat 2nd - C#, 2nd - D, minor 3rd D#, 3rd - E, 4th - F, flat 5th - F#, 5th - G, minor 6th - G#, 6th - A, minor 7th - A#, 7th - B, then back to 1 or 8 - C )

So you pick the 1st of the octave wich is offcourse C then the 3rd is E and the 5th is G. So when you play a C chord you play only those note, with the C being the base note. You add other C's, E's and G's on other strings to make it more "full".

So if you want a Cm7, instead of using the 3rd of the octave u use the minor 3rd and you add a minor 7th.

All that, I didnt know last year. I went threw all the videos in the guitar fundementals 1 and 2 here and got myself a book on music theory applied to the guitar.

So first step, guitar fundementals video series. Very helpfull !
Have a fun journey learning :)