Reflection happens when a wave bounces off a boundary between two materials. One example of reflection is the image above below ⬇⬇⬇.
The light wave in this image is reflected in the water. When sound waves are reflected, they form what is called an echo.
Absorption happens when a wave loses energy as it goes through a material. This can happen in a medium or at the boundary between two materials.
When a wave is absorbed by a material, its energy turns into a different type of energy, such as thermal or electric. One example of absorption is when light waves if concentrated on a spot can begin a fire.
When absorbed, sound waves cannot be heard anymore. This can happen when you shout in a sound-proof room used for recordings.