first you need to install the openssh-server package on the second computer:
$ sudo apt-get install openssh-server
if such a package is already installed, nothing “terrible” will happen.
most likely, both of your computers are in the same broadcast ethernet segment. because you can get to the second computer by its ip-address.
You can find out the ip-address on the network interface in the gnu / linux operating system using, for example, the following command (an example of its output is also shown):
$ ip a | grep 'inet ' inet 127.0.0.1/8 scope host lo inet 192.168.0.123/24 brd 192.168.0.255 scope global wlan0
here 127.0.0.1 is the address assigned to the lo interface (the interface name is the last word in the strings), this is the local loopback interface. and the address 192.168.0.123 is the address assigned to the wlan0 interface (there may be another number and the name is somewhat different: for example, wifi0 , etc.).
at this address you need to connect using the ssh protocol using the first program, for example, the putty program.
when connecting, you will need to specify another username (and, of course, the password of this user). if you do not know the name, you can recognize it, for example, with the command:
$ whoami
after a successful connection, you will receive a working shell ( shell ), where you can perform any actions to manage your second computer.