Irradiation is a very important concept to master, and we utilize for a few reasons.
1. It allows us to create tension, and apply stress on lines of connective tissue. Our biological makeup of tissue responds to stress inputs. In weight training we utilize dumbbells, barbells, and other weighted equipment to apply stress on lines of tissue. Though in a lot of our mobility drills we don't have an external weight, so we must learn how to create stress through our own internal environment and nervous system. We also want to progressively overload lines of tissue by applying more stress, though we do this gradually through weeks and months of training. When you get to the classes, go at your own pace and build up confidence at lower intensities, and then build up from there.
2. When we irradiate and move through ranges of motion, we're developing neurological control over our body. We're teaching the nervous system how to control our joints in space. We're also teaching the nervous system how to produce force. Which is a huge element of gaining strength.
3. It allows us to minimize compensations elsewhere. The goal is to build our joints in isolation. Creating irradiation will help statue the rest of the body, as our targeted area work in complete isolation
The nature of these type of mobility drills (that we do in class) will place the level of difficulty on each individual. The self-effort comes through the form of irradiation. Though if you're new to these concepts, it's always best to lower the intensity at first, and slowly build up from there. Listen to your body and go at your own pace. 
Play around with this and do the drill from the video to get a better feel for irradiating.