cmd.exe: the set command

In its basic form, set creates or removes cmd.exe variables. If a variable is created, it also assigns a value to the variable.

Create a variable (named text), assign a value to it and use the variable in an echo statement:

C:\> set text=Hello World
C:\> echo %text%
Hello World

Delete the variable:

C:\> set text=

set /a evaluates (simple!) mathematical expressions

set /p to get input from a user and assign it to an environment variable.