To add many people to a campaign, you can make use of the bulk create related records feature to add them as a "campaign members".
1) Filter the people you'd like to add to a campaign in Beacon, and select them.
2) Click the vertical dots icon, and choose Create related records.
3) Select campaign members (as we want to bulk create campaign members for these people)
4) Choose the fields that you'd like to set on each of the new campaign members that will be created. Importantly, make sure you set a campaign!
5) Click Create
6) The campaign members will now be created. If you've selected a lot of people, this might take a couple of minutes. When finished, you'll see this message:
That's it! The people will now exist as "campaign members", and will be visible on the campaign record: