I have a problem to find area from a known perimeter of a irregular shape.
For example I have a shape measuring 255m. How much will be the perimeter in meter? Please show me how to calculate the area from this known perimeter?

No more information? It's not possible to solve. For example, if we assume a plane figure (reasonable, right?), and you were trying to maximize the area, you would choose a circle:

P = 2 \pi R

\frac {255}{2 \pi}=\frac {127.5}{\pi} = R

A = \pi R^2

A = \pi (\frac {127.5}{\pi})^{2} \approx 5174.5

On the other hand, let's pick a narrow rectangle of width 1.

W = 1

L = (P-2W) \div 2 = 253 \div 2 = 126.5

A = LW = 126.5

Big difference between 126.5 and 5174.5