"Don't think of Linux as Windows
Numerous people wrote to say that for installing and updating
software, it's a mistake to think of Linux in the same way as one
thinks of Windows. In Windows, you often install software via a
self-contained installer file. Seth Rattan was particularly helpful
in explaining that Linux uses a repository system in which software
necessary for installation or update is stored in an online
repository, which your version of Linux then contacts. At that
point, installation or update should be simple and automated. More
on this when I write a follow-up article.
"Know your distro
Unlike in Windows, you'll generally need to install a version of
software specific for the Linux distribution you're using. Once you
know that, you can seek out software specifically written for your
distro. As "Luis" puts it succinctly in a comment: "The Ubuntu
default package is .deb. Download anything with this extension and
Ubuntu will install it. Just click on it."