Music is written in notation that includes a staff  (five horizontal lines), ledger lines, time and key signatures, and other symbols that tell what notes are to be played and how long they are to be played. In addition to notes, rests of varying lengths are used. They are represented by certain symbols, and appear in measures when needed. It’s very common to have both notes and rests in a single measure. Measures and bar lines (the vertical lines separating and defining a measure) give written music its structure.
Placement of notes occur on the staff of five lines and the four spaces between them. Notes that occur above or below the staff are marked with ledger lines. It’s this placement that determines the note’s name (pitch). For example, the note on the top line of the staff (treble clef) is the note F. The note in the second space of the staff is the note A. Notes of three or more played together are called chords and they appear as notes “stacked” on top of each other.
The notes used in modern notation are either “natural,” “sharp,” and “flat.” These words refer to the pitch of a note. For example, the notes Db (flat), D, and D # (sharp) are different notes (tones) from each other.  On piano, for example, the three notes are played in adjacent keys, left to right.
A musician must not only know how to play the notes displayed (such as the pressing the corresponding keys on a piano, or pressing the proper valves on a trumpet), but how long (duration) the note is to be played. Notes are measured in note values (length of time) using a system of ovals, dots, stems, and flags.
The time signature of a piece of music appears at the beginning of each line. Common time signatures include 4/4, 3/4, 2/4, and 6/8. The first, or top number, represents beats per measure. The second, or  bottom number, tells the musician what kind of note gets one beat. In other words, 3/4 time means there are three beats to a measure and a quarter note receives one beat. 6/8 time means there are six beats per measure and an eighth note receives one beat.
A number of different clefs are used to indicate how the music should be read. These include the G or treble clef, the C or alto clef, and the F or bass clef. These clefs tell the musician on which lines, spaces, or ledger lines the notes will appear. For example, in the treble clef, the first line of the staff is the note C. In the bass clef, the note on the first line is G. Most piano music is written for both clefs with the left hand playing (in general) the notes of the bass clef and the right hand playing the notes of the treble clef.
Music’s rhythm and tempo are determined by beats per minute (bpm) and the use of various words and phrases that define the style of the music. Other terms such as pianissimo and forte tell the musician how loudly or softly to play a note or passage. Also, there are markings that direct the musician to repeat a section, go back to the beginning of the piece, or to jump ahead to a certain point in the composition.