In batch files, you can launch programs. For example, a batch file might need to launch Microsoft Paint, Calculator, and Notepad and thus contain the lines
mspaint calc notepad
However, these programs won't be run at the same time. Notepad will run only after you close Calculator—and Calculator will run only after you close Paint.
If you want the programs to be executed at the same time, you can use the Start command to run them. In this example, you'd include the lines
Start mspaint Start calc
in the batch file.
Another way to launch programs simultaneously from batch files is to use the pipe (|) symbol. The pipe symbol is designed to transfer the output of one command to another command for use as input. However, when you use it in the line
mspaint | calc | notepad
the result is the simultaneous execution of the three programs.
Learn more from "Using URLs in Batch Files" and "How to launch a program before the shell (Explorer) starts."