Key signatures are essentially labels which tell musicians what scale, or scales, a composer used to build a piece of music.
To really know each key, you must know the scale it represents. Thus, keys and scales should be learned together. (The study of keys and scales and chords on the piano provides a great illustration why the piano is the best possible instrument for teaching and/or learning the foundational elements of music theory. With the piano, the images are clear and distinct. Every scale and chord and key can be pictured on the keys of a piano more easily and comprehensibly than on any other instrument. A piano player can improve all areas of his/her understanding of music theory, while at the same time mastering the geography of the keyboard. These things will only make the pianist more capable in all areas of piano music: reading music, memorizing music, and especially improvising and composing.)
Here you will find each key listed with a picture of the major scale and the minor scale it represents. (Right hand fingering for pianists is included.) For more on scales, go to "Piano Scales" .
Once you've learned and mastered the scale for each key, it will make more sense. Playing a piece of music becomes easier when you already "know" the key in which it is written.
All instrumentalists should have the keys and scales memorized. However, if one cannot think of any particular key, here are a couple of tricks.
-The last sharp listed (going from left to right) is always the 7th note of the major scale. Therefore, naming the note a half-step up from the last sharp will give you the key. (A whole-step down from the last sharp will give you the minor key.)
-The next-to-last flat (from left to right) is the key. (This applies to all flat keys, except the key of F which only has one flat.)
Minor keys are always the sixth note of the major scale.
This is just one topic of many from the wonderful world of music theory.