1. What does it mean?
The activities and enjoyment of being a fan: following an artist's work, discussing a series, collecting related items, or exploring a favorite interest in depth. 덕질하다 is the verb form, roughly 'to do fan stuff' or 'to be into a fandom.'
Also written or said as 덕질하다
2. The nuance
'Stanning' fits some contexts, but it can sound more intense than the Korean speaker intends. The activity does not have to involve buying merchandise. 입덕 describes becoming a fan; 덕질 describes the ongoing interest.
3. Examples
“퇴근하고 좋아하는 밴드 영상 보면서 덕질하는 게 즐거워.”
I enjoy indulging my fandom after work by watching videos of my favorite band.
“굿즈를 안 사도 내 방식대로 덕질할 수 있지.”
I can enjoy being a fan in my own way without buying merchandise.
Sources
Edaily: Korean fandom expressions
References support the meaning and usage. Example sentences are written for NoCapWiki.