My friend have a custom server that we play alone, he don't have it online for everyone. I want to control the server too, especially to open the server from my computer and close it. I don't know how to do that and an admin I know told me that his computer and the server are linked so to do what I want I must link my computer to the server so I can open and close the server too. Can someone help me to do that please I would appreciate it alot because he only can open the server only 2-3 hours a day and not everyday. Thanks.

I think what you're looking for is something called Remote Desktop. There are plent of tutorials on how to use it and can be found on google.

Thank you alot

I checked remote desktop, like teamviewer right? To open the server his computer must be on. But what I want to do is open the server from my computer and use my computer for running the server. 

Then just copy paste the server to your computer.

you can share your files with many programms, google drive, one drive... so when your friend will close the server he upload the files on google drive and then you will download them, maybe you can run the server from google drive's folder and they upload automatic, i dont know