Web Content is powerfult abstraction to public web articles and pages in Liferay CMS, but on the moment this entry is created there is no way add web content type. In order to be able to use custom content type you have to add the following line to file liferay-portal-a.b.c-ce-ga1/tomcat-x.y.z/webapps/ROOT/WEB-INF/classes/portal-ext.properties:
where new type is ID of your newly created type, don't use scpecial characters here, keep alphanumeric
and translation to language file liferay-portal-a.b.c-ce-ga1/tomcat-x.y.z/webapps/ROOT/WEB-INF/classes/content/Language-ext.properties:
NEW_TYPE=Name of new content type to be displayed
Restart your liferay insallation to apply the changes.