It is really easy!
1. Open the folder with the rar files.
2. Find the one file among the multiple rar files that has the extension .rar (and not .r09 or anything else)
3. Right-click this file and in the contextual menu which pop-up choose "Open with > VLC media player"
The video will start playing directly, no un-compressing / unraring needed.
If you can't see the file extensions, follow these easy steps to have windows show file extensions.
Click the Start menu. ...
Type "folder options" (without the quotes) and then press Enter. ...
A dialog box with the title "Folder Options" will appear.
Click the "View" tab.
Click to uncheck the box for "Hide extensions for known file types".
Click the "OK" button at the bottom of the dialog box.