How do i do number 1 and 2? i've tried them several times, but i still can't get it.

For question 1, you need to look at the number and decide on the closest square numbers.
For this example, the two closest square numbers to 160 are 144 (12²) and 169 (13²). 
Therefore, we can say that the square root of 160 must be between 12 and 13.

For question 2, when we find the area of a 4-sided shape, we have to multiply the 2 adjacent sides. In this case, as the shape is a square when we multiply the 2 sides it is this same as squaring 1 side. This means that when we find the side from an area of a square you take the square root.
We found in question 1 that 13² is 169, therefore the square root is 13 and the sides must each be 13 ft long.