If you downloaded an Amiga game, then you most likely have one or more Amiga floppy disk image files in ADF, ADZ, FDI or DMS format. These files can be used with any version of Amiga Forever, including the downloadable Value Edition. Once the Amiga Forever player is installed, the games can most often be played with a double-click on the downloaded files. For additional instructions on using these files in the emulation please check the recommended emulation configuration settings as listed on the download page for the specific game, and then refer to:
What's an Amiga ROM, Anyway?
Technically speaking, the disk images containing Amiga games are not "ROMs". Unlike certain game consoles, the Amiga does not use "game ROMs". Amiga software used to be distributed in different formats (floppy disk, CD-ROM, download, etc.), but not on ROM cartridges or on individual ROM chips.
If you are sure that you have an Amiga ROM file, then that is probably an Amiga boot ROM, sometimes referred to as "Kickstart" (like on the old Amiga 1000 computer, where the ROM was on... the Kickstart floppy disk), which contains a minimum of operating system functionality allowing the Amiga to start and then load remaining components from disk. Amiga Forever already includes the required ROMs, so you do not need to install any additional ROMs if you have Amiga Forever.