Some of these may be "proprietary" and exclusive to a particular program, while most are common among many programs.
There are a number of alternative tools which can unpack those types of archive files, but each archive tool has mutiple "formats" in which it can compress a file. (You can use the site to look up those you are not familiar with.) The ones most commonly used for mods on the "Nexus Mods" site are ".7z" (created by the 7Zip program), and ".rar" (created by the WinRAR program. The "file extension", the characters after the last period (".") reading left to right in the filename, indicate which program was used to create the archive package. You may need to place your cursor over the "Vault Boy/Girl" head icon (if any) before it will display the version information.Ī "mod" is a package (archive) of related files that make some change to the vanilla game (including official "Down Loadable Content" (DLC) expansions as delivered by the publisher).
Just to clarify: "Fallout New Vegas" (2010) still uses the same "Gamebryo Engine" as "The Elder Scrolls III: Morrowind" (2002), "The Elder Scrolls IV: Oblivion" (2006), and "Fallout 3" (2008). This article broadly covers things you should know, and points you to more in-depth articles on particular subjects.
If you are new to using "mods" with games on the PC, or just want some tips on how to quickly get using mods with "Fallout New Vegas" (or FNV as it is known) with the least amount of hassle, this is the place to start. The wiki article Installing Games on Windows Vista+ covers the reasons and procedure for moving Steam games.
Save yourself a lot of potential frustration and grief in the future by taking the time to move your Steam game (and really all games that did not come already installed) to a different location. Many unexplained problems are directly related to this location.
If you aren't aware as yet, it's pretty much universally recognized that the default install location used by Steam (to the "C:\Program Files" folder tree) is a problem area due to the anti-malware security measures taken with it since the release of Windows Vista.