Constructing Bent functions of 8 variables I have gone through many literature on bent functions but could not find even a simple examples of creating bent functions. One theorem say like this       If $f(x)$ and $g(x)$ are two bent functions of $V_n$ and $V_m$ them $f(x) \oplus g(x)$ gives bent function of $V_{m+n}$. Can i get any example of creating bent function on V8 by xoring bent function on $V_6$ and $V_2$?   Basically if $V_6$ is having vars $x_1$ to $x_6$ and $V_2$ from $x_1$ to $x_2$ then how we will have function on $V_8$ having $x_1$ to $x_8$. 
Any reference to document which generates bent function with example will be helpful to me.
You cited the theorem wrong. It is:
If $f(x)$ and $g(y)$ are bent, then $f(x) + g(y)$ is bent. The difference is, that the functions are not on the same variables. Otherwise you could use $f(x) = g(x)$, and then you get $f(x) + f(x) = 0$, which clearly isn't bent.

By applying above theorem multiple times, this should be bent:
$f(x_1,\dots,x_8) := x_1 x_2 + x_3 x_4 + x_5 x_6 + x_7 x_8$

I would suggest studying this presentation by Sihem Mesnager, where sections 5 adresses direct constructions and section 6 adresses secondary constructions (built from other bent functions):


Slide 30 has explicit direct constructions
Slide 42 ff. has the above theorem and other constructions from bent functions. Interesting: Slide 44 has a constructions of three bent functions over the same variables.