Did I do somthing wrong?

I just got cc and was excited but when I put down a computer it said "Error mounting lua/rom. Check that you have Installed Computer Craft."
What did I do wrong here? If cc was not installed than how did i put down a turtle?
Is it no compatable with a mod or somthing?

This is usually a symptom of unzipping the mod. The mod is able to be loaded, but the Lua assets aren't where they are expected to be. To solve this, download a fresh copy of the mod and copy the .zip file directly into the mods folder. If you are on a Mac and use Safari as your web browser, it "helpfully" unzipped the file the first time you downloaded it, so be sure not to let it do so the second time.

Yes you did something wrong, don't extract the zip file.