For best results, always keep your Circuit's firmware updated using Novation's Components website. Older versions of the firmware may not work properly with Patch Base.
You can connect your iPad directly to the Circuit via a USB cable and Apple's Lightning to USB Camera Adapter (or for the newer iPad Pro with USB-C port, you would use Apple's USB-C to USB Adapter). When you do this, you should see "Circuit" as options for both MIDI In and MIDI Out in Patch Base.
Alternatively, if you are using a MIDI interface for your iPad, you can connect via the Circuit's MIDI In and Out ports, just as well.
The Circuit uses NRPN MIDI messages to send parameter changes. You don't need to know what NRPN means, but this means that if you're using Network MIDI to connect your iPad to the Circuit (with a computer in between them), you'll need to use Better Live Routings, because the built-in Live Routings for Mac (and Windows, I believe) has a bug that messes up NRPN messages.
The Circuit editor in Patch Base gives you full editing control over all parameters of the 2 Synth voices in the Circuit. You can also load and save banks of 64 Synth voices using the bank editor.
The Main tab holds most of the parameters for a Synth patch. The first 15 Mod Matrix destinations are available from the Main tab, to make routing easier. For access to all 20 Mod Matrix destinations, see the Macro/Mod tab.
The Macro/Mod tab gives access to the 8 Macros for a Synth patch, as well as all 20 of the Mod Matrix destinations.
Patch Base doesn't currently support management of Drum patches, Samples, and Sessions for the Circuit, as Novation doesn't currently publish a way for 3rd parties to access and manage these settings.