I am learning process builder, I am getting confused then what is the difference between process builder and workflow. I mean when to use workflow and when to use process builder? If possible please explain me with examples.
A pretty complete overview with examples of which automation tool to be used in which case can be found here.
In short, you can do everything you can do with workflows using process builder as well, except for sending outbound messages with point&click. With process builder, you can also update all child records starting from the parent record, which is not possible with workflows (only vice versa is possible using cross object field updates). I’ve heard rumors that process builder will replace workflows in the future, which seems a logical step to take for sfdc.