This tutorial introduces Kirchhoff’s current law (KCL). Kirchhoff’s current law states that the algebraic sum of current flowing into and out of a node (or wire junction) is zero. When writing an expression for this conservation of charge entering and exiting the node, we can either write current in = current out, or pick one direction to be positive and the other to be negative, and sum up the current in all branches to zero. It's nice to pick current flowing in as negative, and current flowing out as positive, and draw unknown currents as flowing out. If you find the current to be positive, then it is truly flowing out, but if it's negative, then it just means it's actually flowing into the junction.