This is kind of tricky not knowing how familiar you are with the commandline, but a batch file simply contains single commands and executes them in order (usually from top to bottom). A batch file (or bash script in Linux) can be very helpful if you have to run certain commands over and over again, so you don't have to write them by hand.
An Example: You want to store your network settings in a text file.
You open the command prompt (WIN+R) and type this line:
Then you type this line:
ipconfig /all > C:\Network\ipconfig.txt
The first line creates a folder on your C: drive called "Network"
The second line runs the ipconfig command and saves it as a text file in that new folder.
To make a batch file, you open Notepad and insert the two lines. Then save it as "IP.bat" (make sure not to save it as "IP.bat.txt
"! This is the most common mistake. If you save a file from Notepad, select "All Files" in the "Save As Type" dialog. Otherwise it will save it as a .txt file and you have to rename it later.)
Now you can double click the batch file and it runs all commands in the file.
You can also see the danger. If you run a batch file and don't know what it really does, it can destroy your whole system. So make sure you understand it and/or get it from a trustworthy source.
A nice example of how complex a batch file can be is here:AllHelp.bat
Copy the content into a text file, save it as AllHelp.bat, run it and it will create a webpage with all available DOS commands.
Hope this helps - otherwise let me know if you have specific questions.