To start building your circuit details, in the 'Circuit Details' section of the form, tap 'Click to create circuits'
On the left you will now be able to see 'Origin of Supply' displayed at the top and a '+' icon at the bottom. Tap the '+' button to open the circuit menu.
From here you can create a single phase board, a three phase board or insert a template such as an RCD.
Once created, select the board by tapping on it. You will then see an option to edit circuits - this is where you can then add further circuits etc.