On Mac, click the latest installer, which is the one on top of the list. You will also know if it is the latest by looking at the version number on the installer download link. A new tab should open. Click the gray “Proceed to Download” button near the top center of the page. This should initiate the download.
Alternatively, you can click the downloaded file on the bottom of your browser’s window to automatically run it
Adobe Reader shouldn’t require any customization, so you can just keep clicking “Next” and wait for it to finish installing. It may download a few more files that it needs to be able to work.
PDF files are the usual format for product manuals, some instructional documents, and the like.
If it doesn’t open, you can right-click the PDF file as an alternative. Then select “Open with” in the context menu that comes out. A list of programs that can open the file will appear. Choose Adobe Reader and click “Open” in the bottom right. The PDF should open up, and you should be able to view the contents and even print the document.