How do I get a list of installed files from a package?

To see all the files the package installed onto your system, do this:

dpkg-query -L <package_name>

To see the files a .deb file will install

dpkg-deb -c <package_name.deb>

To see the files contained in a package NOT installed, do this once (if you haven't installed apt-file already:

sudo apt-get install apt-file
sudo apt-file update

then

apt-file list <package_name>

See this question for more

@drysdam dpkg -L <package_name> might be the best for your immediate problem, but you might like to read the Filesystem Hierarchy Standard, which describes where different types of files live in the filesystem.

It is not definitive; it is just a descriptive account of the way things "mostly" are.

More specific to Ubuntu is the Ubuntu Server Guide, which will describe everything in enough detail. (So many of the other guides gloss over too many of the details, but this should be better.)

if you just want a single installed package, you can find the package name

$ apt-cache search rabbitmq
...
librabbitmq-dev
...

then use dpkg --listfiles

$ dpkg --listfiles librabbitmq-dev
/usr/lib/x86-64/librabbit... 
. . . 

The answer given by @Gilles is very useful (actually, the answer was improved over time).

Furthermore, I have a tip for the ones that don't want to install any auxiliary package (like the apt-file):

• Go to http://packages.ubuntu.com/;
• Go to the Search package directories session;
• Insert your package name in the Keyword field and select Only show exact matches;
• Select your distribution and click in the Search button.
• Select the desirable package in the next screen;
• In the end of page, click in the list of files link next to your architecture name;
• The next page will show the list of files of your package.

As an example: http://packages.ubuntu.com/trusty/amd64/multipath-tools/filelist

Here's one way to do it for packages you don't have installed yet. Just change "autoconf" below for the package you are trying to get the list of files for:

mkdir tmp
cd tmp
apt-get download autoconf
ar x *.deb
tar tf data.*
cd ..
rm -r tmp

Use the synaptic-package-manager:

Assuming that we'd like to locate the files of the autotools-dev package, under 'Quick filter' enter autotools-dev to locate it. The autotools-dev package appears automatically. Select it by clicking on it and then press 'Properties'. In the appearing dialog, select the tab 'Installed Files'.