I downloaded the file, but now I can’t find it.
If you didn’t specify a location for the file to be stored, it was probably put in a common downloads folder. Usually they’ll be in a folder called “Downloads,” but once in a while it will go to wherever you downloaded to the last time. Occasionally downloads go to the Documents folder. Browsers often have a quick link to the download folder—test that using CTRL+J.
If you still can’t find the file, the easiest way to remedy that is to redownload using a right click (control click on a Mac) to “save file as” and tell the file where to go.