I just learned this song by G.F. Handel "Sonata No. 3"- Second Movement, and there are these signs that I don't really understand what they mean. I'll give an example: the notes that are to be played is D E F G A.....(D to be played on the A string and E as open string if it were played as first position). The part that gets confusing is that on top of the staff there is a big bold letter saying A. My question is does this mean that the phrase is to be played on the A string as third position? I mean, that was my first guess but then, there is this other place with the notes G A B C...(G to be played on the D string and the A as open string if it was in first position) but then at the top of the staff there is the letter Band there is no such thing as B string right? So my question is what does this sign mean? And if this sign doesn't have to do with shifting in, then what sign would tell you when to shift in?
Can anyone please give me an answer fast? Thanks!!!

I think those letters just divide the music into sections - Section A, Section B ... I sometimes see this on orchestral music, it's a lot easier to tell everyone to start from section B than to have people counting bar numbers.
About shifting into positions, you just have to look carefully at the finger numbers - like if D on the A string had a number 1 above it, you would be playing that note in third position. Hope this helps.

the letters are rehearsal cues - you will find the same letters in the piano accompaniment. they make rehearsing easier! usually instructions to play on a particular string are given in roman numerals- G=lV D=lll A=ll and E=l. But-just to confuse I've come across some pieces which use this system for advising of position changes!
Hope this helps
Anita

The only thing is that this piece is already in grade six and they don't really give you the fingering anymore...

by grade 6 you should be able to think for yourself and begin to work out position changes etc

And very handy these letters come in too! I remember our ambitious university conductor putting on a concert where we turned up and sight read Beethoven symphonies 1-9 end to end before a bemused and somewhat migrant audience. When the Chorus mooched in for Beethoven 9 it all went more pear shaped than before and I recall the conductor looking up to the Chorus somewhere in the middle and shouting, "Letter B!". Not our finest hour. However in rehearsals such conductor-speak as "one-two-three-four bars after letter C" is a useful way of telling everyone where to start together.

it is, if you all have the letters/numbers and they are all in the same place!!