Circuits and Feature Circuits do exactly the same thing, except that Circuits are connected to relays and Feature Circuits are not. Circuits are normally used to control external things that need 120 or 240 VAC power, such as Single Speed pumps, lights, blower motors, etc. Feature Circuits are used to control Internal things, such as VS pump speeds, valve movements, anything that the main board controls.
You can use a Circuit to do anything that a Feature Circuit does, but it would just be a waste of a relay.
Once you program one action, things start to fall into place.
Circuits are fixed and can't be changed.. Such as Aux1, 2, 3, 4, etc and Feature 1, 2, etc...
Circuit Names are what you call a Circuit so that you know what the circuit does.. So you can Name Aux 1, "Pool Lights" or anything else you want.
Circuit Functions only need to be used for specific things... They are used when you want to tell the automation that this Circuit is special. A good example is if you have IntelliBrite lights.. The system has to know these are special lights so that it can control them using the right on/off cycle of the relay. I recommend that you never use a Function unless it is absolutely needed. You can always add it later.. Functions can cause weird problem and are not needed in most cases.
If you have an IntelliFlo VS pump, it is controlled by serial cable and not a relay, so the IntelliFlo's AC power does not go through any relay. It is wired from the breaker directly to the pump.
It helps to pretend it is 1960.. There is not much in common between Pentair programming and today's computer programming.
The builder had the basics for circuits (Pool, spa, lights, blower, etc) but I was getting confused on the scheduling. Basically you have to take your main circuit (Pool) and have that run at the lowest speed you want, then you can add feature circuits that run at higher speeds.
For example, my Pool circuit comes on in the morning and shuts down at night. Within that time that the pool circuit is on, I also added a Skim High circuit that comes on for a few hours in the morning and evening and runs for higher RPMs than the normal Pool Circuit.
Obviously the IntelliCenter has much better graphics than the EasyTouch.. This pics shows the difference... What I like about this pic is that it shows the link, between Circuits, Circuit Names, and Circuit Functions.