You access the membership summary by clicking on CiviMember on the CiviCRM home page. There are two items underneath the CiviMember menu item - Find Members and Import Members (Click on the links for information on those functions).
When you click on CiviMember, you will be brought to the CiviMember home page.
Below the overview messages you will see the Membership Summary:
This table provides a summary of Membership Signup and Renewal Activity, and includes shortcuts to view the details for these commonly used search criteria. The summary displays aggregate membership signup and renewal activity for the current month, year-to-date, and since inception. Signups are sub-totaled by Membership Type.
This page also includes a list of recent member signups and renewals.