How to install libpng and zlib

Open terminal by CtrlAltT

For libpng, run:

sudo apt-get install libpng-dev

For zlib, run:

sudo apt-get install zlib1g-dev

Ubuntu uses a thing called apt, which is a package manager. It installs, manages, upgrades, and removes programs. If at all possible, you should try to install programs via Ubuntu Software Center. What you were likely attempting to do was install from source, which is only recommended if you know what you're doing.

Try to get out of the Windows mentality, which is to search google and download an installer. The Ubuntu Software Center searches Ubuntu's online repositories, which are generally guaranteed to work. Programs installed via Software Center or apt will also be updated automatically by Ubuntu's Software Updater.

You can install libpng from the Software Center by searching libpng and choosing "PNG Library - runtime". Or from here libpng12-0 Install steam-launcher by clicking "available on the Software Center". Or using sudo apt-get install libpng12-0 from a terminal.

The zlib1g package should be installed automatically when you install libpng12-0, because it is one of the libpng12-0 package's dependencies. The package manager apt installs all of a package's dependencies before it installs the package.