Please give us some advice on TTY's understanding and doubts.

For some understanding and doubts about TTY, please give us some advice-general Linux technology-Linux programming and kernel information. The following is a detailed description. Brother, I am developing some gadgets under VxWorks. Although I have been developing on this system before, I did some upper-layer applications at that time, since the company platform encapsulates the interface of the operating system, it does not care about how to implement the underlying layer. so I didn't take care of these things. Now I have to build my own platform to find that I don't understand anything.
For TTY, I understand it as a management of data between input and output, and formatting the input data based on different terminal properties, it is converted into modules that can be recognized and parsed by other functional modules. in a general vswitch or vro system, this is true for the command line input and output through a serial line terminal or a control terminal. in addition, in such a system, the output of LOG/DEBUG and other information, the echo of input commands, and the implementation of Historical query functions. the TTY module is used to manage data.
For Linux (I have read the relevant documents and kernel code, but I still don't know much about it ). for the local Serial line terminal, when the Serial port is initialized, the TTY read, write, open, and other operations are registered to the Serial module and called during data transmission. the same is true for Telnet. Once the TCP/IP link of Telnet is established successfully, the daemon on the server creates TTY and registers a series of operation functions. I don't know if this is correct, but I don't know exactly when Telnet or Sereal is used to open a TTY, when can I write data to the TTY module's read_q? I have never figured it out. I hope you can advise me.
Also, for Telnet/Serial, how do they know what kind of standard terminal device the other side is? After knowing this, do they need to set the terminal properties of the TTY module? In another Telnet mode, do I directly transmit the TTY data to the TTY module, so that the TTY module can process the data through line rules? Because Telnet itself can perform some operations on the input raw data, such as converting the carriage return to line feed, line feed to carriage return, and erasure.
I have said so much and have no understanding. I have all my doubts. Please give me some advice.