To store your favorite locations, like home or work, you need to be a registered Yahoo! member. If you don't have a Yahoo! ID, visit the sign-up page.
After you are registered and signed in to Yahoo! Maps, click the 'chevrons' button on the right side of the address entry box. A dropdown will appear and allow you to see your recent locations as well as Save and Edit any locations you have and label them (for example, "Joe's house" or "the gym") for easy access.
After you have entered your favorite locations, scroll down and click "Finished" to return to Yahoo! Maps.