If you are uploading a file or planning an outreach, here are the required fields.
Mandatory fields:
First name
Last name
Required for campaigns:
Email IDs (if its an email campaign)
LinkedIn URLs (if its a Linked campaign)
Note:
LinkedIn URLs have to be basic LinkedIn URLs, not the sales navigator ones.
While uploading a CSV, if you do not have Last names, simply copy the First name into a new column and rename the column as Last name.