How do I change Sprites (and manipulate the Sprite Object) in C#?

I know it's been asked several times, but I can't find a solution that works. To make things simple, if I use the sprite renderer component and put it in my script, how can I assign a sprite to it? I've seen examples that work--kind of. They assign Sprite objects to the GetCompenent, which works, but the Sprite object is just an empty object and it changes the sprite to nothing--obviously. How do I do this? How do I assign an actual sprite to a Sprite object? (Is there a way to do this without using an array and without using a component to import all the sprites?)