Add a Group to a Campaign
Click the People Tab.
Under My Groups, select the group you wish to add to a campaign.
Click Add Group to Campaign.
Since you're adding to a Marketing campaign, skip selecting a "from" address. You can however choose to add more contacts. If you choose to, click Individuals and type them in. Click Next when done.
Select Marketing Campaign.
Click the Workspaces drop-down and choose the workspace that contains the campaign you want the group added to.
Select the desired campaign and click Next.
You're shown the contacts that qualify. Click Start to get them added.