How to make a connection by command

Could I make a connection between my server and my client without GUI?I try to make a connection by some code or command,but I can’t.Could you give me some help?

You can edit the config file by hand (while Syncthing is not running) or you can use the built in CLI, see syncthing cli config devices add --help for example. (Or you can SSH forward the GUI.)

If I add a client by editing the config,it’s meaing that I should restart my syncthing on my server.And if my cluster have no introducer,the transmission speed will be slower or not

Yes.

It depends. Data is transferred only between devices that know of each other. If you want to data to be transferred between two devices you need to add them to each other manually or use an introducer.