I'm imagining the 6x30" piece is for the loop that goes around the neck and one of the 45" long pieces is for the waist ties, but the 3rd one is a mystery to me.
Then again.....
I can't tell, but is the pie-shaped brown section covering a green same-shaped piece? If so then perhaps it is 'lined' in the green. I did one like this that folded the 90 degree angle point over so that the green shows to the front, making a contrasting detail that can be folded the opposite way -- brown to the back -- to make the apron reversible.....like this:
Jan in VA