Short answer
HubSpot's KB: Create associations links existing records, for example contacts and companies with matching Company name. Matching works with single-line text, multi-line text, phone, number, single checkbox and single select properties. For records the workflow creates, set the association in Create record instead. Workflows can also apply, update and remove labels.
1. The actions
Searching the action picker in my demo portal.

2. Use labels
HubSpot recommends labels because they give more management options in workflows. See association labels.