Double Base - Foul Territory

[ChuckElias]

Could someone briefly explain what the orange base is? My 10-year-old daughter is playing softball for the first time and I've never seen the "double" base at first before. And, of course, I was asked to coach first base last game.

What is its purpose? Is either part supposed to be in foul territory? Does the runner have to stay on the white part? If not, doesn't that give them an extra step toward second base? Can the ball pass over either part and still be fair?

I know nothing here, so help me out please? Thanks.