For explanation purposes I'll call Point A (14,-6) and Point B (12,8) the given points.
To calculate the distance between both points you have to calculate the distance between each coordinate over the x and y axis.
Then apply the Phytagoras theorem to calculate its length.
I'll sketch the points:
x-axis
y-axis
Now according to the Phythagoras theorem, the sum of the squared base and the squared heigth of a triangle is equal to the squared hypotenuse:
For this triangle:
The distance between both points is 14.14 units.