Sitecore's campaign manager allows you organize all of your campaign activities. With unique tracking codes for each campaign that can be applied to track external interactions, you are always able to stay on top of all your traffic sources. You can measure contact engagement value across channels and gain access to real-time info with how people are interacting with your site. Tracking these stats over time allows you to figure out which campaigns are have the highest rate of conversion so you can model future campaigns after the ones that are most successful.

Campaigns help you organize your marketing activities into an effective strategy that you can track, monitor, and adjust based on the outcomes you are seeing. Designing campaigns allows you to lay out all activities involved in promoting your products or services and defining the actions you are encouraging visitors to take when on your site. This gives you a comprehensive view into where your advertising money is being spent, where it might be wasted and where it is the most effective so you can shift your activities to get the most out of your efforts. 
There are two main types of campaigns; online and offline.

Online Campaigns refer to the use of digital media like banner ads, social media, email marketing or any online avenue that can bring traffic to your site. You can measure these campaigns incoming traffic by identifying the channels that contacts use to access the campaign and by measuring the quality of traffic from various channels by comparing contact engagement values across channels.

An Offline Campaign refers to more traditional media strategies such as radio, print, and TV. You can measure these campaigns incoming traffic by using QR codes and friendly URLs.

Creating campaign taxonomies will help you better organize and report on your campaigns and allow you be better analyze the effectiveness of each campaign. The four basic types of campaign taxonomies are Campaign Groups, Channels, Marketing Asset, and Campaign Facet. In the Marketing Control Panel you can create your own custom campaign facets. These will describe aspects of your campaigns that are appropriate for your company and industry.