I'd like to get the members' latest activity.

I found this code in ow_system_plugins/base/views/components/users.html :

{capture assign="activity"}

{if !empty($showPresenceList) && !empty($showPresenceList[$id]) && $showPresenceList[$id]}

{if $onlineInfo}

{if (!empty($onlineInfo) && $onlineInfo[$id]) || empty($onlineInfo) }{online_now userId=$dto->id}

{else}{text key="base+user_list_activity"}: <span class="ow_remark">{format_date timestamp=$dto->activityStamp}</span>

{/if}

{/if}

{/if}

{/capture}

But I totally don't know how I can use it to get the latest activity, with the member's ID or username, can someone explain me how to do?
Thanks!