using the password authentication (i do not have private or public key),then after authentication the traffic will be encrypted before to be sent over the network?

I don't know. This is getting beyond me. Find someone more knowledgeable.

lelunicu, you need to go and read a book, online documentation, all this information has been written down, and in far more detail. This is going to be my last post on this thread.

With SSH, everything is encrypted. The major difference between pki and passwords is your password is sent over the network. Your private key never is. To say that there is no public/private key for SSH is wrong. The server always has a private key and corresponding public key. The part that is optional is whether the user has a public/private key pair.

If the user doesn't have a public key, then the server can't determine authenticity and relies on a different mechanism, however the user can always determine authenticity of the server. Do you ever recall connecting to a server for the first time and being told that it's unknown and if you want to add some information to a known_hosts file?

SSH doesn't use certs because its assumed that the person/system who claims the public key is theirs is the person/system you think it is validated when the keys are exchanged. With HTTPS certs are needed because you aren't going to go to Silicon Valley and go to each of Facebook, Microsoft, Redhat, Google, etc offices, collecting public keys.