We present a theory to describe the equilibrium states and nucleation phenomena in ferromagnetic tubular nanostructures. We show that, in a broad range of geometrical parameters, the magnetic state of a nanotube is a mixture of vortex states, at tube ends, and a uniform magnetization state along the tube axis. The incomplete vortex structures confined at the tube ends are growing domain walls which can be set in motion with external fields, current-driven techniques, or thermal assistance. We also show how the well-known nucleation problem can be better understood with basis in the theoretical model presented in this paper.