How to use the Fields Events
In order to setup an event, open your field settings and go to the "Events" tab, here you can add new events to your field or modify/remove the existing ones.
Taking a "Radios group" as an example, you first need to select the case under which the event is going to be triggerd, which is on selecting/unselecting a specific value, set this to "on selecting", then set the value to "y", we want our event to be triggered when the user selects "Yes".
Under "Actions", select "hide" in order to hide another field, we then need to select the element(s) targeted by this event in the "Element identifier", here you can write a field name, or an element id preceded by a "#" or an element class preceded by ".", so assuming we have another text field in the form, and that it's name and id are "text1" & "text1id" respectively, we can write the following in the "Elementy identifier": text1 OR #text1id, and both would give the same end result, the text field will be hidden when the "Yes" option of the radio is selected.