Merge fields like {firstName} and {company} fill in per contact when a step sends.
Open a sequence from "Sequences".
Click "Add step".
Choose "Email".
Click "{ } Variable" in the editor.
Fields are grouped: basic fields, LinkedIn, social and posts, address, scheduling and your signature. Click one to insert it at the cursor.
They work in the subject line too.
A field with no value for a contact is left blank, so write sentences that still read well without it.