Can someone please explain how to install a DAT file and / or updated engine? I have no idea what these are. I have read briefly on DATs, but can find nothing on engines.
That all depends on which McAfee product you have installed. The engine is merely a term used for the part of the software that drives it, makes it work. To install a DAT in the home product, which is where you posted, you have to either allow it to happen automatically or right-click the taskbar icon and tell the software to look for updates. It cannot be done manually.
To update VirusScan Enterprise or the Total Protection Service (TOPS) - not to be confused with McAfee Total Protection for home, you would have ask the question in that area.
The pages you have been reading refer entirely to the business products.