Hello and welcome Andy

Just to add to what Dave has down, the "root" note determines the chord name. E is the root note of the E chord.

I am not sure whereyou are in your studies, and may or may not already know this, but the note "E" can be found in multiple positions on your fret board and therefore you can have multiple positions to make your E chord.

Knowing the root also helps you play appropriate scale(s).

Best of luck with your studies