10x supports 3 types of workspace:
Folder workspace
When you open a folder in 10x it creates a folder workspace. The workspace will contain all files in the folder and sub folders.
A folder workspace is basically a 10x workspace without any persisted settings. You can convert a folder workspace into a 10x workspace by Saving the workspace, you will be prompted for the name of the .10x file.
10x Workspace
A 10x workspace is like a folder workspace except that it gives you more control over which files and folders are included. You can also setup build and debugging commands.
Read more about 10x workspaces here.
Visual Studio sln Workspace
10x allows you to open up Visual Studio sln files.
note: While it isn't possible to change project settings from 10x you can add and remove files from the project.
A sln workspace supports building and debugging (using the Visual Studio debugger)
See also: