I would like to know what the expression "net current" means.
It's similar to the notion of "net force". If you consider all the forces acting on an object, the net force is simply the vector sum - it's the resultant force.
Similarly, the "vector" sum of currents (in is positive, out is negative) gives the net current into the node.
(If you reverse the sign convention above, you get the net current out of the node.)
KCL simply says that the net current into (or out of) a node is zero.
As an analogy, think of a bank account. Cash deposits in to the account are positive, cash withdrawals out of the account are negative. The net money in to the account is just the "vector" sum of deposits and withdrawals.
If "KCL" applied to this bank account, the net money in to the account would be zero which means that whatever amount is deposited is also withdrawn.