Each Version contains different:  

icons, screen layout, and other visual elements 

New apps or features 

Changes to existing features 

"Hidden" improvements that may boost your device's performance  

Play store (Also known as the Google Store) is similar to the apple store but isn't made and managed by apple  

 

Hundreds of Androids to choose from due to different manufracturers  

Differences: The phone is slightly heavier or lighter 

The hardware is different (button layout) 

Each screen has its own unique layout 

Some of the icons look different; for example, compare the two iPhone icons