Traditionally on Linux systems, if you wanted to install a software package, you were required to obtain the source code and compile it using the compiler that was included in your system. This is still possible today, and hardcore geeks will still tell you it is the best way to maintain your system.
This may be true, but it is also more difficult for novice users and less convenient, especially when you need to update a package.
Fortunately, most modern linux distributions include software systems known as "package managers" which allows you to install pre-compiled binaries and avoid all that mucking about.
Ubuntu, being based on the debian distribution uses "deb" packages for installing binary packages.
While it is possible to download a deb file from the internet and install it (like installing an exe under that other OS), it is much better wherever possible to use your distributions online repositories to avoid being plunged into "dependency hell
In ubuntu, the easiest way to install software packages is by using "Add/Remove" on the "Applications" menu.
A lightly more advanced way is by using "Synaptic Package Manager" which can be found under "System>Administration"
On the command line you can use the apt-cache command to search for a package or apt-get to install and remove packages.
To search for a package using a text string;
apt-cache search | grep search_text
To install a package named "package"
sudo apt-get install package
Next we will look at adding extra software repositories.