What is the difference between Chapati and a Paratha?
Chapati or roti -> Made by folding dough and making a triangle shape results in 3 layered indian bread. If you tear the chapati made this way it will show you 3 layers.

Fulka -> Fulka is made by rolling the dough ball without folding it. This results into a 2 layer indian bread. Its easier to make a circle shape using this method.

Paratha -> Paratha is generally stuffed with some filling. There is plain paratha also (without filling). If it is stuffed , it is not folded into triangle during preparation. If it is plain paratha, it can be made either folding or just rolling (like fulka).

Oil added while kneading dough/ making chapati (folding) / while roasting on tawa ,  helps to keep the product soft.