We study the minimal graph equation in a Riemannian
manifold. After explaining the geometric meaning of the
solutions and giving some entire solutions of the minimal
graph equation in Nil space and in a hyperbolic space we find
a link among $p$-harmonicity, horizontal homothety, and the
minimality of the vertical graphs of a submersion. We also
study the transformation of the minimal graph equation under
the conformal change of metrics. We prove that the foliation
by the level hypersurfaces of a $p$-harmonic submersion is a
minimal foliation with respect to a conformally deformed
metric. This implies, in particular, that the graph of any
harmonic function from a Euclidean space is a minimal
hypersurface in a complete conformally flat space, thus
providing an effective way to construct (foliations by)
minimal hypersurfaces.