i can´t find the file of world 1´s background and i´d like to get help on that.
(the simplest the explaination is, the better it is, im kinda new to both the forum and nsmb hacking in general so yeah)

Like the background used in levels or the background for the world map?

I'm guessing the world map so

"ROM File Browser" > root > map > w1.nsbmd and the textures should be somewhere in there, though I suggest using a different program to edit it since NSMBe isn't that good at editing model textures

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"I strikingly thought you would know how but it clearly seems you have no knowledge of hacking" - MiiU 2017

oh yeah thanks, that makes sense, all the w1 textures are in a single file... well now i feel dumb lol