I have created a custom object called meeting summary, and I have a lookup from an event to this object. I want to have a publisher action which creates a meeting summary record related to the event I'm on. So i have managed to create the Global Action which creates the summary record and I have added it to the Event layout BUT when I create a new Summary record via the event action the Summary record and my event are not related. How can I specify that the action will associate the two records and not only create a Summary record not related to any Event?
An Event is always related to something else, as in another object record, by a WhatID and possibly to a contact or lead by a WhoID. What record Id are you associating the Meeting Summary Action with, the Event or the Object that the Event is associated with?
If it's the Event, you also need to create a related list on the Event Page Layout so it has a place for those records to appear. Without the related list, they have no place to be displayed. If you've done that and its not appearing, then you may need to create an Object Specific Action on Event rather than a Global Action in order to get the Meeting Summary Custom Object Action to show up on the Event Record Page Layout.
You would need to create an object-specific action to do this. Object-specific actions are contextual and have access to the record on which they are bein executed. Global actions don't have that contextual context (except for a handful of standard objects that are magically handled by Salesforce, like Account > Contact).
Unfortunately the standard Event object doesn't support object-specific actions; it only inherits the global publisher layout and global actions. So you won't be able to do this with a standard Create a Record global action.