visit ccp14 website. There are several software packages which are free. Often there are manuals available. Either in written form or sometimes also presentations.
Rietveld refinement can be only that successful as the user is familiar with the theory and the software. You can own a racing car but it definitely does not makes you a successful racing driver. In other words, you need at least 10 wrong solutions until you realize they were wrong and you understand how to operate a software correctly.