Try not to let the number of variations of chords daunt you. Yes, there seem to be countless flavors, and therefore shapes, but so long as you remember that they can all be compared to the 'standard' chord, you'll be able to decipher which are which and you'll also be able to (eventually) construct your own chords without needing to refer to a chart.
The standard chord to which they can all be compared is the Major Chord, and it comes in 5 basic shapes on a guitar fretboard. Once you know which numbers are which (as in 1-3-5) you'll be able to literally see how to change flavors. We've already seen that minor chords are really just major chords with a flatted 3. That same simple logic applies to all chords, and their very names tell you what tones you need. The numbers you see written next to those 'complicated' chords are actually telling you which tones to use. You don't need to know the notes' names, just knowing their numbers is enough. Believe it or not, it doesn't take all that long to see those 5 shapes as a cluster of numbers, as sets of 1-3-5s. Once you can, you can then see all other numbers. How? Just by using logic and by knowing the simple formula of the major scale.
For now, though, you can simply remember the shapes in the diagrams. Once we get to the barre chord section, you'll see how handy knowing these few shapes can be.
We've seen that simple, plain old, chords consist of just three scale notes—that's the minimum requirement to qualify as a chord—but you can have more than three. The next note that can be added to the triad (the 1-3-5) is, logically enough, the 7. I say 'logically' because the chords we've seen so far consist of the 1st, 3rd and 5th notes of their scale—the odd numbers in other words—and the next odd number in line is the 7th. The musical term for 'odd numbers' is 'thirds' so we're adding a third above the third above the third above the root... "Stacking Thirds", as they say in musical parlance.
However, just to toss logic out the window, there are in fact two different kinds of "seventh" chords. One uses the seventh note of the major scale, and for that reason are known as 'Major Seventh' chords. The other uses the note one semitone lower and are known as 'Dominant Seventh' and not only do their shapes look different, but their sound and function are totally different too. 'Function' is something you need not worry about at this stage, but sound is always relevant. You will quickly hear the difference between the two. Let's look at Major Sevenths first, which have a 'pretty', jazzy sound.
The green dots show you where to put your finger tips. The red crosses mean 'Don't pluck/play this string'. The blue numbers indicate the best left hand fingers to use.
1 = index; 2 = middle; 3 = ring; 4 = pinkie.
If you compare these to the majors, you'll see that in each case a root (1) has been moved down a semitone to become a 7 (remember that 1 is the same as 8). That's all that is needed to change the chord from major to major seventh. In the case of the Emaj7, notice that the treble string is crossed out with a red X ... that top string is an E (root).
It doesn't sound good to have a root ringing out higher in pitch than the 7 in these chords. Try it and you'll see what I mean. The Gmaj7 shown here is not very easy to grab and is not used very often. We will look at other ways of playing all these chords soon enough. Notice that I've indicated that you can barre the DM7 with your index finger if you prefer.
Once again, the important thing to remember about these five chords is that they all have the same quality, or 'flavor', they are all Major Sevenths. They look different because of the way the guitar is tuned, but they are all made up of the same ingredients, namely the first (1), third (3) fifth (5) and seventh (7) notes of their scale. When you get a group of notes ringing out in the same relationship, they have the same sound quality. Have another look at the scale degree map for the major chords and you'll see how a root has been sacrificed for a 7, which is one fret lower in pitch than the root. The Gmaj7 shown here is not very easy to grab and is not used very often. We will look at other ways of playing all these chords soon enough.