What does "net current" mean?
"Net current" means the sum of all currents, keeping current direction in mind. If there's going 1 mA into a node, and 5 mA out, then the net current is 4 mA out.

KCL says that the sum of all ingoing currents must be the same as the sum of all outgoing currents. Note that this doesn't only apply to nodes, but to any bounded region.