It’s been a long time since I’ve played with Nix, do you still need to maintain a nixfile or whatever? Maybe I just wasn’t “holding it right” but I recall not b

It’s been a long time since I’ve played with Nix, do you still need to maintain a nixfile or whatever? Maybe I just wasn’t “holding it right” but I recall not being able to just pop open a terminal window and do “X install Y” like with traditional package managers which was a turnoff.