Key Signature
A key signature is the set of sharps or flats that is written at the beginning of a piece of music to indicate the key of the piece.
The key signature may be "null" (no sharps or flats), or it can be from one to seven flats, or from one to seven sharps; it cannot be a mixture of sharps and flats.
The key signature says which notes are always altered, and therefore exactly which notes make up the scale of the key of the piece.
The key can also appear at other parts of the music where the key has change.
The effect of the key signature continues throughout a piece or movement.
The use of a one-flat signature developed in the Medieval period, but signatures with more than one flat did not appear until the 16th century, and signatures with sharps not until the mid-17th century.
Baroque music written in minor keys often was written with a key signature with fewer flats than we now associate with their keys; for example, movements in C minor often had only two flats.
http://en.wikipedia.org/wiki/Key_signature
http://ourworld.compuserve.com/homepages/Neil_Hawes/theory11.htm
The time signature appears at the beginning of a piece of music.
Unlike the key signature, which is on every staff, the time signature will not appear again in the music unless the meter changes.
Most time signatures contain two numbers. The top number tells you how many beats there are in a measure. The bottom number tells you what kind of note gets a beat.
The letter C may be used in place of the 4/4 time signature.
A similar C with a vertical line through it can be used in place of 2/2, indicating alla breve or "cut time"; however, this symbol is also sometimes used for 4/2 even as late as Brahms.
Compound time signatures are distinguished by an upper number which is commonly 6, 9 or 12.
The most common lower number in a compound time signature is 8, representing the quaver note value.
This is four four time.
There are four beats per measure and a quarter note gets one beat.
This is two four.
There are two beats per measure and a quarter note gets one beat.
This is three four time.
There are three beats per measure and a quarter note gets one beat.
This also represents four four time.
This is a measure.
To learn more about key and time signatures, check out these sites:
http://en.wikipedia.org/wiki/Time_signature
http://cnx.org/content/m10956/latest
http://en.wikipedia.org/wiki/Key_signature
http://ourworld.compuserve.com/homepages/Neil_Hawes/theory11.htm