in the documentation there is an About Control Plan which give you a good view on this I think, see below where I have extracted some part of the text for triggers. You can not create any own triggers, but by using the trigger type Manual, you should be able to trigger a custom defined action/trigger by using custom events. 

Sample Frequency Triggers

An analysis can be created manually or automatically. To create an analysis automatically, sample frequency triggers are used. Whether creating an analysis for a specific control plan is required or not is a basic data requirement setting in quality management. When triggers are defined, analyses will be created according to the defined trigger type. Different trigger types are used for purchased parts and manufactured parts.

Trigger types used for manufactured parts are:

• Start Shop Order
• Nonconforming
• Time Interval

Start Shop Order

The start shop order trigger prompts an analysis to be created every time the shop order is set to Started status. This trigger is triggered by the Status badge on the Shop Order page. When the status of the shop order is changed to Started, this also triggers the start shop order trigger. Then the analysis will be created automatically for all the control plan lines (data points) connected to the start shop order trigger.

E.g., If you have a control plan manufacturing (as given below) where all the data points are connected to the start shop order trigger: 

When the status of the shop order is changed to Started, 3 analyses will be created automatically by the start shop order trigger. One analysis will include data points 1 and 2 (routing operation no=10), next analysis will include data points 3 and 4, and the last analysis will include data points 5 and 6.

On a related question...is it possible for an outside “machine” to enter these analysis data points in IFS rather than manually entering them?