D Major Key Signature

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

Guitar Chords in D

Guitar chord diagrams above and degree of scale, chord name and notes below make up the key of D Major.
I Major = D Major - D F# A
ii minor = E minor - E G B
iii minor = F# minor - F# A C#
IV Major = G Major - G B D
V Major = A Major - A C# E
V7 = A7 - A C# E G
vi minor = B minor - B D F#
vii- = C#- - C# E G