Using the /p switch with the SET command you can define variables from an Input.

This input can be a user Input (keyboard) :

echo Enter your name : 
set /p name=
echo Your name is %name%

Which can be simplified like this :

set /p name=Enter your name :
echo Your name is %name%

Or you can get the input from a file :

set /p name=< file.txt

in this case you'll get the value of the first line from file.txt

Getting the value of various line in a file :

(
   set /p line1=
   set /p line2=
   set /p line3=

) < file.txt