Assuming you use Windows :)

Open up notepad, write what you need to do in the bat  file, save it as a
.bat file

Eg

Open -> Notepade.exe
write -> javac CompileJavaFile.java
write -> java  RunJavaFile
SaveAs -> RunCompile.bat (in the directory your java files are in)

A .bat file  should have appeared in that directory :) Double click it
for fun and adventure.

First step is > open notepad write command for which you are making file.
Second step> after writing complete command just save with the extension of
.Bat.