We are considering data migration to CiviCRM. We have two CSV files, one has the details of thousands of "individuals" and another has a list of over 3000 needed "groups". Importing process for "individuals" appear to be well documented, but how do we import/create "groups" (including group properties) from a CSV file beforehand.
Welcome to SE!
You could import the groups with the API CSV importer extension
3000 groups is a lot: there may be better ways to represent your data in CiviCRM. How do you want to use these groups?