A net is a collection of connections. Such as one side of a resistor is connected to a capacitor and it is connected to pin 3 of an IC.
All the nets together are called the netlist.
Yes, it is possible, but it is not advisable.
Without a netlist, KiCad does not know how to keep clearances between different connections. Random tracks may overlap with each other. It is also possible to manually create the netlist inside the PCB editor, but it is a bit of a tedious process. Overall, drawing the schematic first is the easiest and quickest way to create the netlist that is necessary for KiCad to work properly.
This is also a recurring topic on this forum, and a very similar question was asked 9 days ago. In that thread I did a few experiments to see what could be done in KiCad.