first you download a mod called Litematica and the thing needed for it. then u download the schematic. u open ur schematics folder in appdata (it only exists after u launch mc with litematica) and take the schematic from ur downloads and put it in the schematics folder. Then open ur world and press M and then press on Load schematics and select it. Then take a stick and press ctrl. after that hold ctrl and scroll until the stick says that ur on paste mode then if u have ur keybinds (keybinds can be found in the M menu) then just press them while holding the stick and boom!. Im not good at explaining xD so i hope this helps.. Btw you need fabric to launch the mods.

added a schematic