The study guide indicates that approximately 13% of the weighting for the Salesforce Admin 201 certification is given to the topic of Analytics, Reporting and Dashboards.
Given that there are 60 questions, you could expect around 8 questions. This is one of the main topics in the administrator certfication, so you must know it well.
Here is an example of a Matrix report. It has been setup to show lead sources by month. Note that it also includes the sum of expected revenue.
Here is an example and description of what a joined report is and how it can be used, using the example of opportunities.