Magnetic structures

Key points

There is an ample evidence about the magnetic field appearing in a form of flux tubes. Thus the strong field is not present everywhere on the surface, it concentrates in certain nests.
Magnetic field couples throught all layers of the solar atmosphere, and couples also to the convection zone.
Field appears in tubes that are thick (e.g. sunspots) or thin (e.g. faculae, bright magnetic elements)
Sunspots are the key phenomenon of solar activity. An evolved sunspot contain the dark inner umbra and a radially threaded outer penumbra. The spots without a penumbra is called the pore. There are many small-scale features that probably originate in the coupling between the convection and the magnetic field -- described by the magneteconvection approach. We observe dark nuclei, umbral dots and light bridges in the umbra and penumbral filaments and penumbral grains in the penumbra.
The magnetic field evolves. It emerges from the depth (check the criterion for the buoyant rise), evolves in the photosphere, and disappears. It is believed that the fragments (dark nuclei) pertain their identity over all lifetime of the spot. According to the current models, during the emergence the Omega loops remains connected to the bottom of the convection zone, whether the sunspot pair actually keeps this connectivity throughout it whole life time is uncertain (note: dynamical disconnection). The field disperses to the surroundings mostly by diffusion by flows. Spots are partly evacuated (="deeper" in the photospher by some 1000 km - Wilson depression), cooler and hence darker.
Thin flux tubes are also evacuated, hence when viewed from the angle, "hot walls" of the deeper layers appear. Hence e.g. faculae are brighter.
Some general properties may be explained already by the simplistic models (magnetohydrostatic), today we have much more sophisticated models that look almost like the real Sun (magnetoconvective models).