Hi, I am a System Admin with no experience in creating Flows or Process Builder. I have found beautiful instructions to do what I am wanting at this post https://developer.salesforce.com/forums/?id=906F0000000MGXTIA4, namely automatically link Email-to-case Cases with Person Accounts (populate the Account Name field in the Case with the same Person Account that is connected via the sender's email address) BUT I need more detail in the instructions! Any help most gratefully appreciated!

The broad instructions from that post are:
1. Create the flow.
2. In the flow, create an input variable for the case id, phone, and email from the web form.
3. Create a Record Create element and create the Contact record (use the Phone and Email input variables)
4. Create a variable to assign the Record Create element's Id result.
5. Create a Record Update element.  Use the Case Id input variable for the field assignment.
6. Use the variable stored in Step 4. for the ContactId field on the Case record.
7. Save and Activate the flow.
8. Update your process to call the flow instead of performing the related object logic directly in the process.
9. Save the new process version / Activate the new Process version.