Some files, when downloaded, need to be uncompressed (unzipped). This is denoted by the files ending in ".zip" or is listed as a "ZIP file/archive".
Open the file manager in ChromeOS, it is located on the tray and is a blue folder icon.
Navigate to the "Downloads" section on the left side of the window.
You will then see the .zip file in the "Downloads" folder.
Right click (Alt+click), and then select "Extract all".
A new folder will appear in the "Downloads" folder with the same name as the .zip file.
The new, unzipped folder can be opened and the files inside can be accessed.
These files (or the entire unzipped folder) should then be uploaded to your Google Drive to prevent file lose if an issue occurs with the device.