I'm sure this question's been asked before, sorry in advanced, I usually answer my questions by searching on the forum but couldn't find an answer....ANYHOW....I've been playing guitar for awhile now and picked up fast but when it comes to music theory, I'm no whiz. I try learning some stuff online but it's kind of hard, like the Circle of 5ths I can't seem to grasp....but I was wondering, I want to be able to play in the key of E if someone says E, like my friend has a harmonica in E and asks me. I know the major scale and minor pentatonic scale, not all of it, just first two positions, so if I just put that scale starting on the 12th fret for E, standard tuning, would that be in key for either scale or only certain scales? Thanks a lot for your replies guys, it really helps. Also, does it really take long to memorize the whole fretboard, I want to do that soon because it'd be A LOT easier I would think to do anything, also any tips for going about doing so. THANKS A BUNCH GUYS!
I love music. That is all...
The minor scale and the major scale are completly different. If you play the major scale at the 12th fret the you are playing in E major but if you play the minor scale at the 12 you are playing in E minor. There are 5 pentonic patterns that you need to learn and the major and minor are just two of them. Most guitar solo's are worked out in minor anyway so you dont really need the other three just yet, but it looks great being able to play over the whole fret.

My tip is dont bother learning every note on the fret board, just learn the 5 patterns and were the root note is. Than you will be able to play in any major key and its relative minor or the other way around. If this dosnt make sence just ask around there will be heaps of others who can explain better than i can.
What the hell is the internet?
??? i dnt quite understand if ur asking "where do i put the major pentatonic to make it E" then the first note wants to be on the E, so yes, 12th fret.
thx for the response guys, i was kinda meaning like, if i play the major scale from the 12th fret, so E major, and i play the minor pentatonic on 12th fret, so E minor, are they still both in the key of E or does the key of E kinda mean just major, if they said E minor, id use minor scale, or WILL the minor scale still work in the key of E? kinda hard to word sorry, i just want the scale to sound good in the key of E, wondering if thats ONLY major or can be minor scales too....
I love music. That is all...
It depends if your playing in major or minor. If your playing in E major and you want to use the minor scale you will use E majors relative minor. Which of the top of my head is C#minor or Dbminor there the same thing but you get the idea. Dose that help.
What the hell is the internet?