Hey there! I'm happy to help!
To find the distance between two points, you find the difference between the x values, square that, find the difference between the y values, square that, add the two numbers you got, and then find the square root.
We find the difference of the x values.
0-4=-4
Square it.
-4²=16
We find the difference between the y values.
2--1
2+1=3
And we square that.
3²=9
We add the two numbers we got.
16+9=25
And we find the square root.
√25=5
The distance between these points is 5. Now you can find the distance between any two points! Have a wonderful day! :D