Sprites are not just a carbonated drink that many love to drink on a hot day, they are also the little objects that make up a game. A circle can be a sprite or Master Chief in Halo could be a sprite.
The term sprite seems to be derived from the French word esprit or spirit and the latin spiritus. It is a better word than say: dobbie or nixie or even puck. Spirit is defined as the animating or vital principle in man and animals. So in game design your sprites are the animating vital principle in your game. When you deal with the set of sprites that you choose for your app you need to make sure that there is continuity in the underlying appearance.
Here is a set of disjointed sprites along the rows but match (sort of) in column. As a developer you can build your game using “like” art you find someplace and then use that for the artists to work from. That way you don’t waste money on art you won’t use. The way this works is that as a developer you find art that might work, prototype your game and then pull in artists or shop for art that works.
To use sprites in your game design you may need to use tools to clear the alpha channels, size, etc.
One of the tools you could use is Paint.net, there are many: