Bar Chord Extensions - E Shape

Quoting McNoah:

could someone help me? what's the difference between a seventh chord and a major seventh chord? isn't it the same as an E chord and an E Major chord or is an E7 Completely different from an EM7?

No - the chord names aren't totally consistent. What is usually called an E chord is an E Major. It contains the notes E, G sharp and B (a major triad, comprising the root plus a major 3rd plus a perfect 5th). An E7 chord contains a 7th as well but it's a minor 7th (a D note). An EMaj7 chord also contains a 7th but it's major 7th (a D sharp).