How to work with parameters? How can I work with parameters in Blender? I tried searching on Google, but I didn't find results. 

When I change the parameter on the X and Y axis, it works well, but when I go into Edit mode, I can't see the parameters. And when I extrude, I can't adjust them on the extrusion. How can I work with dimensions and how to make the parameters in real world scale?
First set the Units in the Scene properties to Metric or Imperial. If you are using Imperial, then checking Separate Units can help make it more natural.

For 2.8x 

For 2.7x 

When entering in units in Object mode using the Dimensions, watch the scale. You have to apply the scale ( ctrl A > Scale ) before the same measurements will show in edit mode. When the scale of the object is applied (all three field set to 1)  then dimensions will work as excepted in edit mode.