How do I know what packages I need to install?

Solution 1:

Use

$ apt-cache search <mysearchterm> <othersearchterm>

to search for packages matching these terms in the description field. For example, let's say you're looking for a PDF viewer for use in KDE, you could do this:

$ apt-cache search pdf viewer kde
okular - universal document viewer

Then use apt-cache show <pkgname> to show more details:

Description-en: universal document viewer
 Okular is a universal document viewer with support for advanced document
 features, such as annotations, forms, and embedded files.
 .
 This package provides the document viewer application, plus plugins for a wide
 variety of document formats such as:
  * PostScript (PS)
  * Portable Document Format (PDF)
[...]

Alternatively, use any other package management tool that you like. E.g.:

• aptitude (ncurses-based semi-GUI in terminal)
• synaptic (GUI)

They all provide similar search functionality which is more user friendly than apt-cache search.