Even though we computer experts do seem pretty magical to non-experts, we still need a proper description of the error message to tell you what's wrong and how to fix it.
I'll still take a guess and say that you're not using the proper combination of versions. If you're playing Factorio 0.15.???, then you need Factorissimo2 version 2.1.9, and if you're playing Factorio 0.16.???, then you need Factorissimo2 version 2.2.1.
Try clicking the "Check for updates" button in the mods screen, and then the "Update mods" button. That should fix everything automatically. If not, try it again a few times (because the mod portal is spotty), and if it still doesn't work, then come back and tell me the version numbers of the "Base mod" and "Factorissimo2" mods that you can see when clicking on them in the mods screen.