When sea waves reach an obstacle, a very small part of the incoming energy is dissipated in heat through viscous effects. In certain conditions (breaking), another part is dissipated in spray. If the obstacle is fitted with openings, another part is transmitted through them. The remainder of the energy is reflected. The direction of reflection depends on the incidence and on the slope of the bottom, because the wave celerity is linked to the water depth
as well as to the wave period.
The superposition of incoming and reflected waves creates "standing waves" in front of the obstacle. The analysis is made more complex by the fact that natural waves are irregular: a sea state can be described as the superposition of an infinite number of individual regular waves, each with its own direction, period, height and phase.
A more detailed description would not fit the "for dummies" requirement. For pictures, see for example www.csun.edu/~aes15831/subjects/Oceanography/unit8/powerpoints/L09_Waves.ppt
Describing the flow of current
around an obstacle is another matter.