The Event Rule Set Entrant Event will add the contact to the Journey funnel when that contact matches the rule set you create. This process is the same as when you perform Searches or create Segments in the Contacts section of the application. See Fig 1 below.

Fig 1

To add the specific ruleset to the Journey, click the Event Rule Set  entrant node once you have added it to the Journey work area. Doing so will bring up this popup ("Properties") on the right-hand side of the screen (See Fig 2 below):

Fig 2

Clicking the "Add Condition" button will bring up a popup very similar to the ruleset popup used to create Search and Segment rulesets. See Fig 3 below.

Field #1 allows you to select the list membership, basic default field or custom field you wish to evaluate.

Field #2 provides several operators (depending on the specific value you have selected for Field #1) by which the system will evaluate the value of Field #1.

Field #3 is the value or state of Field #1 being evaluated.

Again, as with Searches and Segments, you may have more that a single ruleset as part of the total ruleset group by clicking the small green circle with the white "+" in its center. Doing so will add another trio of Fields. 

Fig 3

Once the "Event Rule Set" has been defined, click the "Save Properties" button at the bottom of the popup. The popup will close. To close the Properties popup without performing a selection, click the small "X" in the top right corner.

If you wish to remove an Entrant Event, you may click the "Delete block" button at the bottom. However, please note you must have at least one Entrant Event in a Journey for it to be valid. If you try and delete the only available Entrant Event, the system will show an error. If you wish to replace the Event, select a new one from the list in the left side menu and drag it into the Entrant Event node area in the work area first, then you can delete the other Event.