I have theoretical result, as an output of MATHEMATICA program, and experimental results, as an excel file, I want to find out the easy and quick way for fitting process of both results, theoretical and experimental.
Click on Help in the menu bar of Mathematica and subsequently click on Documentation Center. Using the search box, search for 'Interpolate'. Use the search results to inform yourself about the available possibilities that suit best your application. Look in particular into the function 'Interpolation', which is very straightforward to use.