how do i create an iso file?

hi i just tried to download a ngc rom but it's not a .iso file how do i change it to .iso so that dolphin can read it?

What type of file is it?Dolphin can open ELF, DOL, GCM, ISO, WAD.If you just downloaded it, it might be compressed/archived in some way, RAR, ZIP, etc.

it's a .zip containing a bunch of files

.zip is a zip file, needs to be un-zipped. Open it with WinRAR, and extract the files.