Microsoft Windows machines implement a mechanism that permits connecting from outside and remotely controlling them.
By default a desktop PC has this disconnected + there is a port that should be opened in order to this mechanism to accept connections (numbered 3389). Individual routers have this ported closed by default through another mechanism called NAT
Therefore a single laptop with Windows, won't be "accessible" via RDP unless A) You activate this service + B) You "open" the port in your router linking to your laptop IP address
Also the PC has to be ON in order to RDP to work, because the RDP service has to be active. By default, if you activate RDP service, it will activate as soon as you boot (you don't even need to input your credentials)
This said, online servers that 24/7 ON and are Windows based, have RDP service activated. Also the "router" they use, have all the ports opened by default to that machine, therefore most people that rent a VPS can connect through RDP service without much hassle.
Just FYI, if you have a GNU/Linux online server get to know that the alternative to RDP is called SSH.
PS: Many people call Windows VPS "RDP", but this is a wrong definition. Windows VPS has the RDP Service activated and "available" by default, but they are not RDP if you have understood this explanation.