I downloaded my file, but now I can't find the file on my computer.

When you download a file from the internet, the file gets stored in a folder on your computer. Normally, when you click a download link, your computer / web browser should ask you where you want to store the file. If it doesn't, it's because you have set up your operating system or web browser with a pre-determined location (download directory) for storing downloaded files. Check your web browsers' "Options/Settings" screens. See if you can find something about where the browser will store downloaded files.

(Tip: in Mozilla Firefox, press Ctrl-J. Firefox will show you a list of recently downloaded files. You can right-click on any one of them and choose "Open containing folder". That will open a new window that displays the folder in which the file was downloaded.)