Ubuntu is open source software and (almost) anything with a .deb extension
can be installed just by klicking on it. However, over 25,000 tested, bug
and virus free programmes and libraries (like dll's in Windows) have been
collected and put into online 'repositories' by Canonical.

You can find word processors, graphic editorial, music and video players
etc. etc. Many are fully equal in quality to paid software for other
operating systems. You do need a fast internet connexion, although linux
software tends to be compact and not bloated like that for some other
operating systems.

You access them with an included app called 'Package kit' or something
similar, which lists and allows searching and installing. These are all
safe choices and you would do well to only use programmes from this trusted
source until you are more familiar with k/ubuntu.

Many of us prefer to install using 'Synaptic', also available in the
repositories, as it is more powerful.
Much more could be said, and will be, but this should get you started.