What this is:  Polonaise in F major by J.S. Bach, BWV Anh. 117a

What to look for first:  Key signature and time signature.

Things you will probably recognize:  Eighth notes, quarter notes, sixteenth notes, time signature, key signature, bass and treble clefs.

Things you might not:  Mordents, accidentals and grace notes.

Short breakdown:  This is a piano piece for two hands in F Major, as made evident by the one-flat key signature.  It is also in 3/4 time, which means that you can expect there to be no more than three quarter-note-length beats per measure. 

The mordent is the squiggle-shaped mark above the first treble-clef note of the first two measures.  It is played as a turn, sort of half a trill going from the upper note to its lower neighbor and then back. 

You will notice that there is one flat and one natural added into the music.  This means that the composer is expecting you to play a note that is not in the standard scale of the key signature.  For example, in the second measure, there is a B natural.  Since F Major includes the b-flat, this is a change in the key and is therefore called an accidental.  The same goes for the e-flat in the third measure.

Grace notes are the small notes tied to the certain larger notes.  In many types of music, these come before the beat as a very short note.  In the time that this piece was written, you would play those two notes for an equal duration, so instead of playing a grace note and an eighth note, you would play two sixteenth notes.

What this is:  "Ave, Verum Corpus" by W.A. Mozart

What to look for first:  Key signature and time signature.

Things you will probably recognize: Quarter notes, half notes notes, time signature, key signature, bass and treble clefs, crescendo and decrescendo.

Things you might not:  Dynamic markings, ties.

Short breakdown:  This is a choral piece with lyrics shown here in both Latin and German.  It was written for a SATB (Soprano, alto, tenor and bass) chorus.  The bass and tenor lines use identical rhythms, but the soprano and alto lines are vastly different.  The alto line alternates between mimicking the men's lines and following the rhythm of the sopranos. 

The sopranos and altos sing a number of tied notes, which are the ones connected by an arc.  This means that all of the notes between the two points of the arc must be sung on the same syllable of the word that corresponds to it.

In terms of the dynamics, the piece starts out at piano, but in measures 5-6, there is a crescendo and decrescendo.  This is an increase and decrease and volume, up to the discretion of the choir conductor. 

Also, the large figure that looks like a "C" in place of the time signature is a marking meaning "common" time.  It is therefore in 4/4 time.