The OSI model is a fundamental conceptual/reference model that was created by the International Organization for Standardization to describe network communication. OSI stands for Open Systems Interconnection. The OSI model is a generic, protocol-independent model. There is another model called the TCP/IP model, but that one is for more specific communication issues and is based on specific standard protocols.
Open Source Intelligence is the act of finding and gathering information from public sources on a target. You’ll probably be surprised by the amount of information that can be found online with a bit of prodding! OSINT is great because it’s typically not very expensive and and can reveal a lot of information about a target. Even something as simple as checking a company’s posted job requirements for an open position can reveal what technologies and systems they use, which can help in finding a vulnerability. Something to watch out for, however, is fake information that may be posted.
TryHackMe has a couple of networking basics modules that are meant to teach the fundamentals of computer networking. I’ve taken a couple of intro networking classes already, but I’ve found THM’s format to be exremely easy to understand and great for learning/review!