For the chief musician

"This is for the director of music to use in worship"

set to Shoshannim

This may refer to a style or the tune of the music. Sometimes it is translated as "set to the tune of 'Lilies.'"

"This is a psalm that the sons of Korah wrote."

This may refer to a style of music.

"My emotions are excited about a good subject"

"a noble theme" or "a beautiful word." This refers to the song that he has written.

to have written or created a song

"my tongue is like the pen of person who writes well" or "I speak words as skillfully as an experienced writer can write words"