I am a small part of a larger picture. If I am missing, the picture isn't whole. What am I?

What has many keys but cannot write a single word? Solve the riddle → I have a big mouth and collect things you throw away. What am I? Solve the riddle → What has rings but no fingers? Solve the riddle → I fall from the sky but have no wings. I make puddles and help flowers grow. What am I? Solve the riddle → I fasten papers together using small metal pieces. What am I? Solve the riddle →