Here are the steps to follow when assigning contacts to a campaign on the web:
Note: Your contacts must have an email address for them to be assigned to a campaign.
1) Log in to your account
2) In the left column, click 'Contacts'
3) Select a contact - click the 'View/Edit' button or click the name of the contact to view their profile
4) Once you are on their Edit Contact page, scroll down and look for Assign/Change Campaign
5) Click on the drop down icon and select a campaign
6) Click Save