Intro
Verse
Pre Chorus or Chorus
Verse
Pre Chorus/Chorus
Mid 8
Chorus
In it's simplest form. Other styles like Rock, metal and folk musics around the world can be seen using structures similar to this.

What makes this simple format so effective?

The lyrics tend to follow the structure, variating on verses to elaborate upon the story arcs and contexts. The chorus is generally our strong reminder or summary to the songs message and in most cases is the more "catchier" section of the tune that people are meant to remember the most.

This is in no way a global representation, but generally most pop songs exist in 1 key and seldom journey beyond that unless its for a climactic ending in which a song is pushed up a whole tone or a third (as in the ending of Baby Be Mine by Michael Jackson) in the last chorus.
Harmony is generally diatonic, but can utilise other types of harmony like the melodic minor scale like in Beyonce's "Single Ladies."

Instrumentation is very varied as the term "Pop" is largely defined by cultural norms and what's current at the time in the main-stream media. Generally it utilises the whole spectrum of musical "voices" of a time or era and can exists anywhere from being the sounds of an acoustic singer/songwriter or someone using a computer to create backing tracks that are heavily MIDI or sample based, musics like EDM and Hip Hop, which all have songs that feature under the pop umbrella at sometime or another. Sonically the sound of Pop cannot be defined by any one category of instruments, because it exists across many genres and time period that where all "popular" at one point or another and is in essence the most diverse genre of music in terms of instruments used, how many are used and for what purposes they are used for.

Being a creation of culture, the main rhythmic and melodic ideas come from whatever is current at a time. The ideas of Pop are usually very basic to follow and don't exclude anyone in terms of understanding the context of the song, how it comes across or is heard by the listener. The experience is meant to be easy going, and does not pose any "sophistication" threats that come from more harmonically advanced musics like Classical or Jazz. Pop music sees to unify people more and delivers music that can be enjoyed by the majority.