Select the column in the current table in memory to use an an index value (like a campaign_id), then select the reference Table or Worksheet as well as the index column that contains matching values (like id).
Then select the columns you want to add to the current table from the reference table. To select more than one column, hold the Ctrl-key down while you click.
If more than one row in the reference source has a particular matching index value, you can select how you want to handle those duplicates.
You may have a table of email campaign clicks with a “campaign_id” column:
And you want more information about that campaign. You also have a worksheet containing Campaign data, but the campaign id column is labelled simply “id“:
You can select the campaign_id and id columns as the Index, then select the name and modified_date columns from the list (as per the image above).