If you are new to Lightroom or maybe just want to understand something there is a free Lightroom download which helps to understand how to use the program and describes exactly what it does, available from the Lightroom Queen . You will need to add your email details to the site in order to download the document either for Lightroom 5 or 6. You can always unsubscribe after downloading if you want.
There is also a wealth of information on the web with lots of excellent videos. I have found the ones by Julieanne Kost very helpful.