Flour: : Flour is the main ingredient in pastries. There are different types of flour you can use to bake - depending on the recipe you have. Some examples are plain flour, self-raising flour, french flour, bread flour etc. Due to its solid form, it enables the pastry to have its form and shape.
Self-raising flour already contains raising agent in it. Therefore there is no need to add baking powder
Plain flour has no raising agent in it so baking powder must be added to it when baking unless the recipe specifies otherwise. Flour must be sifted properly for aeration purposes and measurements taken after sifting as flour has the tendency of increasing in volume after sifting
See conversion/ measurement to know equivalent