Through UI, you need to register a portlet to portal-managed applications prior to adding it to a page. By configuration, it is not required.

Assume that you already configured a site and some pages by site extension. To add your hello-portlet to a page, you just need to modify pages.xml to add the following configuration:

<portlet-application>

    <portlet>

        <application-ref>hello-portlet</application-ref>

        <portlet-ref>Hello</portlet-ref>

    </portlet>

    <title>Hello</title>

    <access-permissions>*:/platform/users</access-permissions>

    <show-info-bar>false</show-info-bar>

    <show-application-state>false</show-application-state>

    <show-application-mode>false</show-application-mode>

</portlet-application>

So the whole file looks like this:

<page-set xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://www.gatein.org/xml/ns/gatein_objects_1_2 http://www.gatein.org/xml/ns/gatein_objects_1_2"

  xmlns="http://www.gatein.org/xml/ns/gatein_objects_1_2">

    <page>

        <name>homepage</name>

        <title>Home Page</title>

        <access-permissions>*:/platform/users</access-permissions>

        <edit-permission>*:/platform/administrators</edit-permission>

        <portlet-application>

            <portlet>

                <application-ref>hello-portlet</application-ref>

                <portlet-ref>Hello</portlet-ref>

            </portlet>

            <title>Hello</title>

            <access-permissions>*:/platform/users</access-permissions>

            <show-info-bar>false</show-info-bar>

            <show-application-state>false</show-application-state>

            <show-application-mode>false</show-application-mode>

        </portlet-application>

    </page>

</page-set>