You have to setup "Public member profile" for the members that you want to show on Member directory.
See Public member profile section on the following page: http://help.wildapricot.com/display/DOC/Adding+a+new+member+record
and http://help.wildapricot.com/display/DOC/Customizing+member+public+profile
To change it:
Go to the member profile and click on Edit button. Scroll down to Public member profile section and put checkmarks on every Detail that you want to show. Right now they are not permitted to show any details.
You can also do a bulk change by using Import-Export.
See: http://help.wildapricot.com/display/DOC/Export+members+list
and http://help.wildapricot.com/display/DOC/Import+Guide