What is a protein shake and do i need one?

I want to spend my summer getting built! At first i didnt plan on buying protein shakes but now im taking it into consideration. The thing is, do i have to make a whole shake with a blender and fruit plus the protein powder and milk and yoghurt every single time? Im not really sure how it works but can i just put the protein powder into a bottle of water, shake it up, and thats it? I also am not sure if i really need one but to me they sound very effective, taking into consideration im only 15!