Forge should automatically query this file when you start Minecraft and display a small blinking emerald on the "Mods" button in the main menu if your version is older than the latest recommended version:
Same should go for pre-releases if you currently have a pre-release version installed. If the latest version is a release version and you'd like to be notified of pre-releases, there's currently no mechanism for that afaik.
There's no mechanism for snapshots other than regularily checking the thread in which I've recently posted a snapshot link (I usually post snapshot links only in specific threads for specific purposes, e.g. specific, low-priority bug fixes or the 1.14 version).
The thread which contains a summary of all changes for each update should be linked on the Download page (close to the bottom).