A Major Key Signature

Going from the key of G to the key of D, we added another sharp to the key signature, C#.
Now going up another 5th from D to A, we add another sharp to the key signature, the 7th note of our new scale, G#.
So the key signature of A is three sharps, F#, C# and G# and the notes that make up the A major scale are A, B, C#, D, E, F#, and G#.
 

Guitar Chords in A

Guitar chord diagrams above and degree of scale, chord name and notes below make up the key of A Major.
I Major = A Major - A C# E
ii minor = B minor - B D F#
iii minor = C# minor - C# E G#
IV Major = D Major - D F# A
V Major = E Major - E G# B
V7 = E7 - E G# B D
vi minor = F# minor - F# A C#
vii- = G#- - G# B D