I've been reading on packets a lot today. I was confused for sometime because smtp, http, or ftp, for example, are all called protocols. But that they also somehow utilize transport protocols like TCP. I couldn't locate them on the packet 4 layers. Until I just discovered they're simply part of the application layer.
I want to know what exactly these "protocols" offer. I'm guessing a specific format for the data which applications on the client side know how to handle? If so, does this mean that realistically, I might have to create my own "protocols" if I created an application with a unique functionality?
A protocol, in this case, is just a structured way of communicating between two or multiple parties.
If you write, for example, a PHP-App and offer an API, you created a protocol to interact with your program. It defines how others interact with it and what response they can expect while doing so. Your self-created protocol depends on others, like the HTTP and TCP.
I suggest watching following video of LiveOverflow, explaining exactly this: https://www.youtube.com/watch?v=d-zn-wv4Di8&ab_channel=LiveOverflow
You can read the definition of each protocol, if you really want to