The word “green” has been used for a long time to mean “not experienced.” English speakers borrow it from the natural world: a green plant isn’t fully mature, so it represents being early in the process. In everyday slang, “green” becomes shorthand for someone who hasn’t learned the craft—or at least hasn’t learned the local version of it.
When you add “fucking” in front, you’re usually not just saying “I’m inexperienced.” You’re adding heat. That heat can mean embarrassment (“I know I look clueless”), anxiety (“I don’t know what I’m doing”), or humor (“I’m fully aware I’m messing up, but I’m still here”).
There’s also a second layer that appears online: “green” as a vibe of being new and unpolished—someone who still feels like they’re growing. That meaning is closer to the “fresh out of the box” energy, not just the “newbie” label.