Hi Ajay,

Process builder and flows are the two tools to automate the process in Salesforce. In short, both are used to automate the processes but flows are used for achieving greater functionality. Here are quick points regarding each:

1. We use Process Builder when you need to start a behind-the-scenes business process automatically. Processes can start when:

-A record is created
-A record is updated
- platform event occurs

2. We use Flow Builder to:

-Automate a guided visual experience.
-Add more functionality for a behind-the-scenes process than is available in Process Builder. Use Flow Builder to build more complex functionality. Then call the resulting flow from the process.
-Start a behind-the-scenes business process when a user clicks something, like a button.

For example, when an opportunity is won, your company wants a renewal opportunity to be created automatically, you can build parts of that use case as a process, but the rest has to be built in a flow.

For more examples please refer: https://trailhead.salesforce.com/content/learn/modules/business_process_automation/process_whichtool (under which automation tool is right for my usecase.)




I hope you find the above solution helpful. If it does, please mark as Best Answer to help others too.
Thanks,
Ajay Dubedi