If from fresnel a factor is given to the mix shader's node, then is it just a value like 0.5 or so? Or does it produce a value which is not of type of numeric values like 0.5, 0.2 etc. If i'm totally wrong then i would like the proper description of it. Thanks.
The fresnel node dynamically affects a mix shader's factor value. It's not a constant value; it's variable across the surface of your model. If you plug in your fresnel value into an emission node (to see the raw color value visualized) you can see the black-to-white values that dynamically affect the factor. Where black values means a factor of 0 and white means a factor of 1; any greys in between mean values between 0 and 1 for the factor.