As with most software on FreeBSD systems, there are two supported ways to install Enlightenment: via Packages or Ports.
FreeBSD is undergoing a transition to the Next Generation Package format (pkgng). For users unfamiliar with pkgng, The FreeBSD Handbook provides an introduction, including instructions for migrating a system already using the older package format. As the older form is to be deprecated in the near future, I include instructions only for pkgng here; if you are still using the older package format, substitute e.g. pkg_add for pkg install below.
To install E17 using pkgng, the command could not be easier. As root, type:
# pkg install enlightenment
This should be all you need to do to get a basic E17 installation, as dependencies are automatically installed for you. There are, however, also a number of optional modules available for installation. A search of the repository with, for example:
$ pkg search e17
...will display a list of e17-modules, from which you may install your preference in the same manner as the base Enlightenment package, above.
You should probably start by ensuring your ports tree is up to date, using one of the methods described in the Handbook. Enlightenment 17 is in the ports tree under /usr/ports/x11-wm/enlightenment. The most basic installation method is to change to the appropriate directory in the ports tree and execute "make" as root; i.e.:
# cd /usr/ports/x11-wm/enlightenment
# make install clean
Alternatively, using the "portmaster" ports management system, the command would be:
# portmaster x11-wm/enlightenment
In either case, any dependencies you do not already have installed will be auto-selected for you.
Note that if you are offered the compile-time option to use "Illume," this refers to the mobile device optimized version of E17, which is probably not a common use case for FreeBSD systems.
Many E17 modules are also in the ports tree, but perhaps the easiest way to approach them is to build the meta-port x11-wm/e17-modules which will then offer a typical compile-time options menu, from which you may choose the individual modules you wish to install.