how can you can use squaring to estimate 7 square root

One possible way is as follows:

Try something obvious to start with

2^2 = 4

3^2 = 9

so the answer is between 2 and 3

Now try the midpoint of these (2+3)/2 = 2.5

2.5^2 = 6.25

This is too low so try half-way between this and the previous high value (2.5 + 3)/2 = 2.75

2.75^2 = 7.563

This is too high so try half-way between this and the previous low value (2.75+2.5)/2 = 2.625

2.625^2 = 6.891

... and so on until you get sufficiently close.