After you've done this, you will be prompted with a Z:\>. Now, just write what you wanted to call your new DOSBox drive, which as I said above, we called C. To navigate to that newly mounted drive just type in:
Z:\>C:
C:\>
Hopefully, you're all set! Now, it's time to run the game. Previously I had mentioned a game called TESTDRIV in my OLDGAMES folder. I now want DOSBox to go to that folder. So type in:
C:\>CD TESTDRIV
C:\TESTDRIV>
That's it! CD stands for "Change Directory", so you've changed the directory to TESTDRIV. You can find instructions on how to use the Change Directory command, in the CD section of the Commands article.
One more step, running the game! Most games have an EXE file in their directory that you can run. However, some might require a BAT file, or COM file (common in demos and really old games). Most of the time, the file is in the root folder. Please consult the documentation of your game for which file is needed to start the game. In the case of Test Drive, it's TDCGA.EXE. So now, I just type this:
C:\TESTDRIV>TDCGA.EXE
(stolen from the Dosbox wiki XD)