You may want to review simplifying roots first.
You can find the distance between any two points. You take the difference between the two x-coordinates (in either order) and square it. Then you take the difference between the two y-coordinates and square it. You add the two squares and take the square root of the answer.
For example, suppose the points are (−2, 0) and (0, 0). Then the x-coordinates are −2 and 0, so the difference is 2 (or −2, if you subtract in the other order). When you square that, you get 4. The y-coordinates are both 0, so their difference is also 0, whose square is still 0. Adding the two squares gives 4 + 0 = 4. Then you take the square root of 4, which gives the answer, 2.
The answer won't always be a whole number. For example, suppose we had to find the distance between (−3, 0) and (0, −1). Then the difference between the x-coordinates is 3, whose square is 9. The difference between the y-coordinates is 1, whose square is 1. Adding the two squares gives 9 + 1 = 10. Then the answer is √10. Don't forget to take the square root at the end, and to simplify it if possible!