This batch file will launch a program (Windows Calculator) repeatedly. The START command launches the program, the WAIT program waits until it's finished. The PAUSE command probably won't be necessary for what you wish to do.
If you remove the "WAIT", you'll get multiple copies of calculator running. In fact, if you let this run without the PAUSE, you'll have more copies of calculator than you can deal with.
here's a link to information on the START command
MS-DOS start command help
:BEGIN
START/WAIT C:\WINDOWS\system32\CALC.EXE
PAUSE
GOTO BEGIN