What is boolean variables and what are the do??

Answer 1

Boolean variables or variables of type "bool" are made to hold two possible values namely:
True(1) or False(0).
The default value bieng false.
They are mostly used in conditional statemests like:
if(x==true){break;} etc.

Answer 2

Booleans are the variables that hold values "True" and "False" (can be used as triggers/switches e.t.c....)