IPFire can be installed in various ways. There are different kinds of images that can be used. Which one to choose depends on the system you want to install IPFire on.
All installation media can be downloaded from ipfire.org.
Each image has both the serial and the graphical console enabled. The serial console is intended to be used on headless systems (no keyboard and monitor).
This is the most common installation option. You will need to burn the image on an empty CD, put it into the machine you want to install IPFire on and boot from it.
USB key (a.k.a., a thumb drive, a USB drive or a flash drive)
As optical discs are getting more and more out of fashion so that many systems do not have a CDROM drive any more you can also use a USB key to boot the system from. For that download the ISO image and write it to a USB key.
Using a pre-installed flash image
Some systems are not able to boot from any other media than the system disk. PC Engines's ALIX is the most prominent example of these systems. In this case you must use one of the pre-installed flash images.
To use one of these images you will need to write it to a flash card.
Booting from network
You may install IPFire over the network via PXE, too.
After you have prepared your installation media, go on to the next step: Step 3: Run the installer