Hey there
HardAtWork and welcome to GeeksToGo,
Well as mentioned above, you may use the script in order to do what you require... Although you are trying to write a batch file (Which would probably be much easier), a batch file is easy enough to write and understand so I'll pop what should go into the contents of the batch file below with brief explanations:
> Firstly you will have to open notepad (Notepad is a basic text editor which will be more than sufficient for writing your batch code in)
> Then copy and paste the code provided below:
@echo off
SET /P folder="Please Enter Folder Name: "
explorer "R:\%folder%\"
The first line "@echo off" is just a key line that will tell the command window that you do not want to output any content of your batch file unless explicitly specified.
The second line is where you ask the user (Yourself in this case) to enter in some form of value and then store that value into a variable. In this case the variable is "folder".
The last line is a call to the "explorer.exe" that takes a command line argument of the folder you would like to navigate to upon opening. As you can see the folder is replaced by the variable created earlier from the users input.
For the scope of what it seems you require I have not gone in-depth in my explanations (Of course if you require further explanation do not hesitate to ask). Also if you were to enter a folder that doesn't exist, explorer would just open to the default folder (Usually Documents).
Peace Out