When a number is squared in math, it means it's been multiplied by itself. For example, two squared is two times two, or four; and 10 squared is 10 times 10, or 100. When a number is squared, it is written as that number (the base) to the second power.
Whether the base is positive or negative, the base squared is always positive. Two positive numbers multiplied together yield a positive product, and two negative numbers multiplied together always make a positive number as well. A square root of a number is the number which, when multiplied by itself, yields the square. For example, the square root of 25 is either five or negative five because either of those numbers multiplied by itself yields 25.