convolution vs correlation? What is difference between convolution and correlation?In simple words or in a nut shell?

As far as i am able to study is that Convolution is a mathematical operation used to express the relation between input and output of an LTI system. It relates input, output and impulse response of an LTI system while Correlation is a measure of similarity between two signals
Convolution:

$$ y(t) = h(t) \circledast x(t) = \int\limits_{-\infty}^{\infty} h(u) \, x(t-u) \ \mathrm{d}u $$

Cross Correlation:

$$ R_{xy}(t) = \int\limits_{-\infty}^{\infty} y(u) \, x(t+u) \ \mathrm{d}u $$

The difference between the two is effectively the sign on $u$ in $x(t-u)$ in the integral.  That correlation is like convolution but with one of the signals flipped left to right is essentially the basis of the Matched Filter.