You access the contribution summary by clicking CiviContribute on the CiviCRM home page. There are three items underneath the CiviContribute menu item - Find Contributions, Import Contributions and Manage Contribution Pages (Click on the links for information on those functions).
When you click on CiviContribute, you will be brought to the CiviContribute home page.
Below the overview messages you will see the Contribution Summary:
This table provides a summary of Contribution Totals, and includes shortcuts to view the contribution details for these commonly used search periods. To run your own customized searches - click Find Contributions.
The summary displays aggregate contribution activity for the current month-to-date, year-to-date, and cumulative.
This page also includes a list of recent contributions. You can sort them by clicking on the headers of the column you want to sort by, for example, clicking on the "Received" header will sort contributions by the date they were received. You can sort them from newest to oldest or oldest to newest by clicking on the column header.