Depends on where you want to see the application displayed
To display the application on your local PC
You first ssh to the remote computer with the additional
-Y option and the run the application (e.g. firefox):
ssh -Y ...
-Y doesn't work check you sshd config on the remote PC (see Denis Lukinykh's answer). Another similar option is
-X. Google for the differences.
To display the application on an existing session at the remote PC
You need to login with user A at the remote PC and leave the session open. Afterwards you can ssh with the same user A and start the application (e.g. firefox) like this:
DISPLAY=:0 nohup firefox
To display the application nowhere
You need to install & start xvfb. xvfb will create an invisible X session at
DISPLAY 10. Then you start your application directing its output to that
sudo apt install xvfb
sudo Xvfb :10 -ac -screen 0 1024x768x24 &