If you have chosen to make the member directory protected, it will display to those who have a member level user account or higher. After logging into the website, they may view the directory by clicking Content link on the Admin Bar, from the drop down menu click on Member Directory.
You can also create a navigational or other type of link. The link address that you will need to use is directory.php.
If you have chosen to allow people to edit their own directory information, they will be able to access this information by clicking their name on the Admin Bar; from the drop down menu click Edit my Profile. In the Edit User page, they may change their contact information in the Account Detail tab and any additional information in the Directory tab.