Difference between Kratos and Hydra

Can someone, please, explains to me exactly what is the difference between Ory Hydra and Ory Kratos? and a polpular alternative to each one of those so I can really understand the real use case of each one of them which would help me choose what suites more my use case.
I’ve been looking for a proper way to implement a SSO server with oauth2 and I still have some unclear ideas about this subject.
Thanks a lot

OAuth2 is just a protocol, it does not solve login or user management. That’s what kratos does though.

OpenId connect is the protocole that solves this problem and I guess that hydra does implement that

No, OpenID Connect solves Delegation of Authentication, meaning Relaying Party authentication. It does not solve login itself.

Can you please give me more details about that? or point me to a ressource that explains the diffrence between “Delegation of Authentication” and the “Login” itself

Thanks a lot.

OpenID Connect does not define how you store passwords, reset passwords, verify emails, register accounts, …

Fore more insight into OpenId Connect please consult our docs