Could someone please help me with the step-by-step pact broker implementation? If anyone has any detailed documentation, it will be really helpful.

Have you read this:

See this page on the steps to creating an effective contract-testing setup https://docs.pact.io/pact_nirvana. (This workshop demonstrates those principles in action: https://docs.pactflow.io/docs/workshops/ci-cd/)

And the workshop: howtolearn

Here are a number of useful hands-on labs that teach all of the key concepts: https://docs.pactflow.io/docs/workshops and https://docs.pact.io/implementation_guides/workshops