It makes a array of pixels. By default it will set all of them to no color.
But if it sees that in the provided pixels arg it contains the (x,y), it will change to the color provided.

Example:
(x,y): Fore.COLOR GOES HERE

Function Example:
        
render(
    {
        (x,y): Fore.COLOR GOES HERE,
        (x,y): Fore.COLOR GOES HERE,
        (x,y): Fore.COLOR GOES HERE
    }
)
or
render(
    {
        (1,3): Fore.RED,
        (4,2): Fore.BLUE,
        (1,1): Fore.YELLOW
    }
)

You can actually run the second one and see what it prints!
