Remote maintenance Raspberry Pi  and remote desktop with VNC, RDP and SSH

here are several ways to remotely control a Raspberry Pi. Remote maintenance or remote service is generally possible via command line (SSH) or desktop sharing (VNC, RDP). Which solution to choose depends on your own requirements.
All solutions have in common that one does not sit directly on Raspberry Pi with a screen, keyboard, and mouse, but operates from a remote computer. You can do that with a desktop PC, notebook, tablet or smartphone.