Accessing file explorer across different networks.

Good Evening,
I have a few questions around a small business I am assisting a friend to set up.
The director of the business has a number of Folders and Files within their Windows 10 PC, and the aim is for the work from home administrator to be able to also view / edit / add to these files and folders.
If they were both logged into the same Wi-Fi network I understand this would be simple, but because they both work at different locations I need some advice on how I can help make this happen. Is there a facility already built into windows or is additional software required? I am fairly confident with windows myself having helped a number of friends and family over the years but unfortunately networking isn't my strong point. I've done a bit of googling around but quite simply I'd like anybody that is granted permission to be able to access the file explorer on the main computer, go into these folders, save items to these folders and so on and so forth.
This is my first post on the forum so I am very sorry if this is a very long winded way of asking a question but any respectful responses would be gratefully appreciated.

Vers. 21H2

Kind regards

Josh

Hi,

If it is only for one user. The most easiest way to do it is to install a dedicated computer for remote intervention, and have the user work remotely on it...

If you want to have multiple concurrent sessions, there is Windows 10 Enterprise multi-session. It is a cost effective way to have Multi RDP sessions without having to buy Windows Remote Desktop Server (formerly Windows Terminal Server).

With the correct licenses installed can be used to accommodate multiple users, at the same time.

The big advantage of using RDP is that files are open locally at the remote site, So opening large documents are seamless because you never have to download the actual file to open it, unlike opening it on a shared drive trough a VPN.