Sounds like you have standard (for the USA) split-phase service (assuming this is a house and not an apartment in a large complex, which might be 2 of 3 phase service).
As @philrob said, figure out what you want to learn. You panel does not appear to be well marked as to what the circuits do. You have four large loads. 11/13 Range, 17/19 (unmarked), 22/24, and 28/30 (unmarked). The unmarked are either, AC, Dryer, Water Heater, Pump. I would definitely put on a water heater as there are things you can do to change your usage and/or learn just how much it costs to heat water. You probably don’t use a range enough to make it worthwhile to measure separately, but maybe. You can learn the usage of them, by looking at the main breaker readings, since the usage will be noticeable. If you have AC, that would be good to measure.
But, it really comes back to why did you buy the IotaWatt in the first place, i.e. what did you hope to learn/change?