What to do with an injured bird?

My mom found an injured sparrow in our backyard and I went out there to see if I could help it. There was a cut under his eye and his left leg looked a little damaged and he kept twitching, but was alive. I cleaned up the blood and put him in a box with newspaper and toilet paper and put him in our garage. Can anyone help me by telling me what I can feed it and how to care for it? (besides calling an animal center, PLEASE don't tell me to do that. I'll do that when I'm sure that I can't help it.)