Hi, @Pritam Roy 

Variant Explorer is fairly intuitive: it represents entire variants, from start to end. It is the recommended tool to analyse end-to-end process flows.

Process Explorer, on the other hand, shows you how many variants have passed through the displayed activities and connections. In other words, it does not represent variants themselves (like Variant Explorer), but rather the number of cases passing through the various activities and connections displayed. Note that the numbers represented in the activities and connections are the respective total cases, and usually are different from the neighbouring ones.

Use the Variant Explorer - Course Outline | Customer (celonis.com)

You can also thinks a variant is a representation of many cases. In the process explorer, we see the collection of many variants.