SUMMARY
If you wish to add a single prospect directly to your campaign, you could do so with Add by profile link tool.
To add contacts one by one to a campaign:
Go to Campaigns from the main navigation menu
Select the campaign
Click on "Actions" to open the action tool selection menu
Click "Add by profile link"
Add person's LinkedIn profile URL
Click "Add"
You can add as many people as you want this way, however - one at a time.
IN DETAIL
To add a single person directly to your campaign, go to Campaigns from the main navigation menu and select the campaign:
Click on "Actions" to open the action tool selection menu:
Click on in Add by profile link action button:
In the pop-up window, paste the individual LinkedIn URL of the person you would like to add to the campaign and click Add:
This person will immediately appear in your campaign and you will be able to reach out to them with campaign sequence messages.
You can add as many people as you want this way, however - one at a time.