How do I see who added a record?

You can see which collaborator has added/edited a record in the record-level revision activity feed. Specifically, to see who added a record, scroll all the way to the top of the activity feed—the first collaborator listed is the person who created the record.

Note that your record-level revision history is limited according to the pricing plan of your workspace. If the record was created prior to the earliest possible date that your pricing plan will show, then you may not be able to see who initially created the record. For more about the record-level revision activity feed, including limits on the record-level revision history, please see this support article.