So when a company first starts out - as a sole trader - then it might be that a company has a single computer, and as there is only 1 person in the company there is no need for a network.
Windows 10 support the concept of multiple users, so it is possible to log into a windows 10 device using a separate username and password for each user.
Each user on that machine will have their own documents folder, and desktop. Files placed into those folders will only be accessible to those users.
Logging in
Ctrl + c
+ Tab