A stream cipher is an encryption algorithm which encrypts arbitrary length plaintext, using a key. Some stream ciphers generate a keystream from only the key, which is then XOR-combined with the plain text, others feed back plaintext or ciphertext into the algorithm to create the keystream.
If you have a TRULY random key (in binary) and you have a text (in binary) that you want to encrypt. Can you simple XOR the key and the text? Is that secure? How secure?