This is a common inquiry, and all the answers are the same but different. IoTaWatt is very versatile and can accurately measure individual appliances immediately. That said, you need to know what you want to measure and install passive sensors for each of those circuits.
There is complete documentation here. It reads pretty quickly. I’m guessing you are in North America, so take a look at the split-phase power discussion to understand better what is inside your load-center. Then run through the first few installation instructions to see what’s involved.
Here are several other recent threads where folks asked the same question:
https://community.iotawatt.com/t/equipment-needed-for-200a-residential-us-installation/1975
https://community.iotawatt.com/t/equipment-recommendations-for-us-residential-200a/1998/10
Assuming you are in North America, at a minimum you would need the Base unit, power supply and AC reference transformer included in the North America Bundle and two current transformers for the mains. After that, you can add up to 12 more current transformers to measure individual circuits or groups of circuits. So it requires some planning to determine what, if any, individual circuits you want to monitor (including solar), and the appropriate size CT for each (50Amp or 100Amp).