Reports: Overview
First, you should familiarize yourself with a general report view:

Most of the options will be available all the time, however, some of them (for example, report categories) are contextual and may change accordingly.
Report Types
The main way to differentiate one reports from another is by the number of elements a report is based on:
Global Report
A report that is based on all elements from a given category is called a Global report. An example of such a report is the campaigns report, which contains information about all running campaigns.
How to open a global report?
To open this report, click a report category.
When should you use a global report?
When you need to get a broader view of everything that is going on on your account. In global reports, you don't have the drill-down option or the Live events category, so the highest level of data granularity is hidden. However, global reports offer a perfect sneak peek into your campaigns' or offers' profitability.
What report categories are there in global reports?
Specific Report
A report that is based on one element from a given category is called a Specific report. An example of such a report is the Sample Campaign specific report. A specific report is opened in a separate tab.
How to create a specific report?
To open it, simply click an element from a report category and click the Report button. The specific report will open in a new tab, next to the HOME tab.
When should you use a specific report?
Specific reports provide the most information about a particular element. They allow you to see live events or use the drill-down option. Use this report type to learn details about a given campaign.
What report categories are there in specific reports?
Filtering by multiple campaigns
You can select up to 50 campaigns and create a specific-style report for all these campaigns.
How to create a specific report?
Select between 2 - 50 campaigns and click the Report or Report in a new tab buttons
When should you use this type of report?
This type of rport is great when you want to see cumulative and detailed data for multiple campaigns.