Answer
IF a>0
$\ \ \ \ $tol=0.000001
$\ \ \ \ $x=a/2
$\ \ \ \ $DO
$\ \ \ \ $$\ \ \ \ $y=(x+a/x)/2
$\ \ \ \ $$\ \ \ \ $e=abs|(y-x)/y|
$\ \ \ \ $$\ \ \ \ $x=y
$\ \ \ \ $$\ \ \ \ $IF e < tol EXIT
$\ \ \ \ $ENDDO
$\ \ \ \ $SquareRoot=x
ELSE
$\ \ \ \ $SquareRoot=0
ENDIF
Work Step by Step
IF a>0
$\ \ \ \ $tol=0.000001
$\ \ \ \ $x=a/2
$\ \ \ \ $DO
$\ \ \ \ $$\ \ \ \ $y=(x+a/x)/2
$\ \ \ \ $$\ \ \ \ $e=abs|(y-x)/y|
$\ \ \ \ $$\ \ \ \ $x=y
$\ \ \ \ $$\ \ \ \ $IF e < tol EXIT
$\ \ \ \ $ENDDO
$\ \ \ \ $SquareRoot=x
ELSE
$\ \ \ \ $SquareRoot=0
ENDIF