Is the keystream transmitted with the ciphertext when a stream cipher is used? When a stream cipher is used and a keystream is generated to be XOR'ed with the plaintext, is the keystream sent with the ciphertext so that the receiver knows how to decrypt it? Or does the receiver(s) need to already know the keystream?

Absolute noobie to cryptography.
The keystream is as long as the message, so you don't want to send that to the receiver. The keystream is generated by a much shorter key (e.g., 128-bit private key). That is what the receiver needs in order to decrypt the message.

So, how do you get that to the receiver? Well, clearly you can't just send it in the clear or anyone watching the channel would have the key and could decrypt. Typically what we do in cryptography is run a key establishment protocol. This could be as simple as Alice and Bob meet up and exchange the key on a written piece of paper or as complex as using asymmetric crypto, with public/private key pairs, certification authorities, etc.