This sentence means: "He likes listening to music, especially classical music, which helps him relax and relieve stress."

Simple explanation:

* "He likes listening to music" means that this person's hobby is listening to music.

* "Especially classical music" shows that he likes classical music very much, but it doesn't rule out that he also likes other types of music.

* "It helps him relax and relieve stress" means that he thinks listening to music can help him relax and relieve the stress in life or work.