The userprofile variable can be used for this.
There's a Number of 'fixed' environment variables that are static.
In cmd.exe type:
and you'll get a list of all currently set variables - typically all the fixed variables.
The Documents folder is located at
%userprofile%\documents by default.
Generally, though, it's better to create subfolders in your programs folder, relative to the program itself. Even if the folders moved, everything in it stays relative to your main program. However if things created outside your programs folder get moved, your program can no longer access it.
To achieve a relative filepath, in your Main program, before calling any functions:
This expands to the directory (folder) your program is in, and you then make any new folders / files needed within your programs folder.
IF not exist "%Prog_Dir%resources" MD "%Prog_Dir%resources"
Your subfolder will always be at "%Prog_Dir%resources".
Not 100% clear what you're asking with regards to opening a specific folder, so I'm going to make an assumption:
To open a folder in the Windows Explorer GUI:
start explorer.exe "PATH"
where path is the directory pathway for the folder you wish to open.
E.g., to open the user's Documents folder:
start explorer.exe "%userprofile%\documents"
Alternately, you can view the contents of a folder within a command, using:
REM - Will display all folders (Directories) and files in the current working Directory.
cmd.exe for a full list of options (there's a lot).
To view just the Folders and subfolders of a particular directory:
REM - Will display a graphical representation of all Directories and Subdirectories Starting in the Working directory.
REM - A specific Folder to view can be specified using TREE: