  In this brief tutorial review, I show how phase coherent properties of
disordered conductors can be described in a simple and unified way. These
properties include transport properties like weak-localization correction and
universal conductance fluctuations, and thermodynamic properties like orbital
magnetism and persistent currents. They can be related to the classical return
probability for a diffusive particle. For a network with $N$ nodes, the return
probability can be related to the determinant of a $N \times N$ "connectivity"
matrix $M$ so that the magnetization and the transport quantities can be {\it
directly} written in term of $\det M$.
