Learning how to identify cadences is a helpful skill for all musicians. Whether you're relatively new to the language of music or a seasoned player, understanding cadences is important.
Gain a knowledge of key signatures and become comfortable spelling and identifying the I, IV and V triads for each major key (when comfortable with all the major keys, focus your learning on the minor keys and triads). There are a number of sites online that offer information on key signatures and their triads.
Cadences in music occur when a harmonic progression closes a phrase, section or piece. Grab a simple piece of piano sheet music that contains a left-hand and a right-hand part.
Scan your eyes across the music for a stopping point, such as the end of a phrase (usually indicated by phrase markings), section or the last couple chords.
To make things easier on the eyes, take a pencil and circle your choices for your cadences in the score. (Identifying cadence locations requires a lot of listening experience and a fair amount of theoretical knowledge when scanning a score.)
Let's say that the music you're looking at is in the key of C Major and you happen to see a G Major triad (or V triad, spelling G, B and D) resolving to a C Major triad (I, spelled C, E and G). When V resolves to I, we call this an Authentic Cadence. Since the tonic (C) is in the soprano (highest) voice of the I chord, it is called a Perfect Authentic Cadence.
This time around, you'll see the same thing you saw last time: V (G Major triad) resolving to I (C Major triad). You'll notice that the voicings are a bit different and that the tonic (C) is not in the soprano voice. When a member of the I chord besides the tonic is in the soprano voice, we call it an Imperfect Authentic Cadence.
Another cadence type you may come across is a little trickier. Still in C Major, we have V (G Major triad) resolving to vi (A Minor triad, spelled A, C, E). This time, since we expect the strong resolution of V to I, and we get V to vi, we call this a Deceptive Cadence.
Here, we see an F Major triad (IV, spelled F, A and C) resolving to a C Major triad (I). When IV resolves to I, we called this a Plagal Cadence; you may also be familiar with this sound because it is the "A-men" cadence in a hymn.
While scanning a piece of sheet music, it is often helpful to play through the melody to see just where the resting places are throughout. This can offer helpful hints to where the cadences occur. If you're playing a piece on piano, play the left-hand part by itself to hear the harmonic progression. Your ear will guide you as you begin to identify where cadences are occurring. Listen to everything you can; this will help in the development of your musical ear. Sing and play often; music is a language, and repetition and reproduction of common musical ideas will help embed the idea of cadences in your mind. Practice identifying each chord in your sheet music through harmonic analysis or marking in the I, IV and V triads where appropriate.
It is necessary to have some basic to intermediate music theory chops to do this. Knowledge of key signatures and an introductory knowledge of harmonic progression theory (triad spelling) is also necessary.