Zero-G products are download either as ZIP files (.zip) or as RAR files (.rar). A zip or rar file is a compressed archive containing part or all the files contained within the sample pack (for example WAV, REX, Kontakt etc).
Also included inside the zip or rar file is the Zero-G End User License Agreement (which you must read before using the product) and often you will find a PDF included of the booklet that accompanied the physical CD version of that title, and one or more mp3 demo songs.