The March is one of the oldest styles of music. The Military March is a style composed for marching and most often performed by military bands. A typical march contains several melodies.
Most March melodies are spirited in nature that is also very catchy that could easily stay in the listener's mind.

Most Marches begin with an Introduction.
The introduction sets the mood of the music. The introduction is mostly written in four, eight, or sixteen measures long.

The different sections in March music pieces are called Strains which is the verse in songs. Each strain contains one main melody. There are usually three different strains plus the contrasting section called the Trio.

The main melody of the piece with the length of eight to sixteen measures with four-measure phrases. During the second
repeated time of the first strain, the composer will add a second melody known as counter-melody to go along with the main melody.

The new strain introduces the second melody with a length of sixteen measures. The composer always writes this as a repeated section and will usually choose to have a second melody played softer for contrast.

Feature section of the March. This section is usually thirty-two measures long. The tonal center or key signature changes, an immediate change in the dynamic level from loud to soft by the entire ensemble, a new melody is a prominent element that reminds us that the march is in the section of the trio.

The purpose is to produce excitement for listeners and musicians that is used to put a break between the Trio sections or we could understand it as the bridge in songs.

The introduction: the whole orchestra
plays and the brass section carries the melody.

At figure two: the whole orchestra plays until figure three,
when it repeats back to the D.S. (first figure).

The trio: played by the brass section, with the trumpet
playing three sixteenth notes in the last bars.

Figure six: the whole orchestra plays
and then repeats back to figure five.

The orchestra plays until the last bar,
then returns to the D.C. (beginning).

The orchestra plays until figure three, finishing with the Fine ("end") bar— the direction is Da capo al fine (repeat from beginning up to the word Fine).

Sonata form, also known as sonata-allegro form consists of three main sections which include exposition, development, and recapitulation and sometimes include an optional coda at the end.

Sonata form in song structure could be recognized as verse, chorus, verse 2, chorus, bridge, chorus.

Exposition could be also understood as the introduction of the piece, during the exposition the main melodic ideas, or themes, are introduced. There are usually two contrasting themes. The first theme is in the tonic key and a bridge will lead to the second theme, which is in a related but dissimilar key. The exposition is repeated verbatim after closing with a strong cadence in the new key which means that the listener will hear each melody twice.

This repetition is widely used in sonata pieces because these themes will return in other sections.

The development is where new themes and new keys are introduced into the piece. The music modulates to foreign keys, new themes appear, and the melody often sounds much like an improvisation. The themes are difficult to recognize because when these themes appear, they are usually fragmented, turned inside out and upside down. After the development, the recapitulation brings the melody back to the tonic 'home' key. The original themes from the exposition are repeated again, this time, both the first and the second themes are in the tonic key.

The bridge section still serves to connect the themes.
This time, the bridge does not modulate to a new tonal area but remains in the home key, the tonic.

The composers will often choose to use coda to end the piece. The coda section may vary in length depending on the idea of the piece, short coda may serve as an extension of the final cadence while longer coda is used to introduce new themes or further develop the original themes.

In the first movement of K545, measure 1-4 is the first theme and exposition, 5-12 is the transition, measure 13-26 is the second theme, measure 13-15 is the codetta with a mini ending that ends on G on measure 15. Then repetition happens and the performer will have to repeat the following part one more time. Measure 16-31 is the development or bridge of the piece that leads to recapitulation which starts on F major from measure 32-36. The first four measures of the development section from 16-20 are in G minor, the next four measures from 21-24 are in D minor, and finally, the next four measures following 24 from 25-29 is A minor. The transition then happens again from measure 37-49 which theme 2 starting on C major follows from measure 50-67 with a codetta in the end from measure 68-69 then repetition happens again so the performer will have to play the repeat from measure 16 all the way to the end. The last measure ends on a G7-C which is a perfect cadence.