Block cipher encrypts and decrypts the block of text at a time. But Stream cipher encrypts and decrypts the text by taking one byte of text at a time.
Block cipher is best used when you know how large is the message. When you don't know the exact size, it is better to use the Stream cipher.
Block cipher algorithm modes: ECB(Electronic Code Book) and CBC(Cipher Block Chain)
Stream cipher algorithm modes: CFB(Cipher Feedback) and OFB(Output Feedback)
