For entering a large number of contacts from a spreadsheet and creating related cases for each contact, the NPSP Data Importer is the best tool. It allows for configuring upserts (updates or inserts) for Contacts and linking them to related records such as Cases.

Steps:

Prepare the spreadsheet with the necessary data for Contacts and Cases, ensuring all required fields are included.

Open the NPSP Data Importer in Salesforce.

Map the fields in the spreadsheet to the appropriate Salesforce fields for Contacts and Cases.

Configure the importer to upsert Contacts and create related Cases based on the spreadsheet data.

Run the import process and verify the data in Salesforce to ensure all Contacts and Cases are correctly created and linked.