Emaj7 is built from E, G#, B and D#. E is the root, G# the major third, B the fifth and D# the major seventh. Said aloud, its notes are E, G sharp, B and D sharp.
String by string, low to high, it plays E, B, D#, G#, B and E. The root, E, shows up twice in the main shape. The lowest and highest notes are both E, two octaves apart, on strings 6 and 1.
The open strings add notes to Emaj7 too. String 6 gives E, string 2 gives B and string 1 gives E. Your hand covers two frets, from 1 to 2. There is one more position, starting at fret 7.
Change only string 4 in Emaj7 and you have E. Inside Emaj7 sits a complete G#m chord, made of G#, B and D#. Moving to B7, you keep two fingers down.
Emaj7 shows up in four keys. In E major it is the I, in B major the IV and in G# minor the VI. The rest appear in the key list.