Let these three points be A, B and C the vertices of the triangle.
Use Pythagoras Theorem for each pair of coordinates, the root of the sum of the squares of the differences between the x and y coords:
AB=√((2-(-3))²+(2-5)²)=√(5²+(-3)²)=√(25+9)=√34 (x-coord diff=2-(-3)=2+3=5, y-coord diff=2-5=-3)
BC=√((-3-(-2))²+(5-(-6))²)=√((-1)²+11²)=√(1+121)=√122
CA=√((-2-2)²+(-6-2)²)=√((-4)²+(-8)²)=√(16+64)=√80
The perimeter=AB+BC+CA=√34+√122+√80=25.8206 approx.