Xoops CMS files are all packed in a compressed archive, either ZIP or RAR
These need to be downloaded from the website onto your local machine.
You need to decompress the archive, using a standard decompression tool like winzip, pkzip, winrar, or similar.
The decompressed archive will give you one folder with several sub-folders and associated files in them.
IMPORTANT: always maintain the files and folders in exactly the same distribution as they are decompressed in. This is how they should be uploaded and storred on your server in order to maintain correct relationships among the files.
Always look for 'readme' files, or other files that have titles like 'updates', 'changelog', or similar.
Open TXT files in a plain text editor or html versions in your browser.
DO NOT open any other files in WYSIWYG editors or applications like MSword. These often add spurious code that will corrupt your files.
If you upload files to your server, always maintain the exact same distribution, that is all the files in any folder must be maintained. Likewise, folders within folders ... keep it strictly in order.
Using a FTP client is the best option to upload files as you will be able to upload the whole distribution in one go, without worrying about keeping the contents in order. Typically dragging and dropping the folders within html folder into your web-space root will give you a 'root installation'
SEE Xoops installation guide
for full directions...