Erlang is a programming language used to build massively scalable soft real-time systems with requirements on high availability. Some of its uses are in telecoms, banking, e-commerce, computer telephony and instant messaging. Erlang's runtime system has built-in support for concurrency, distribution and fault tolerance.
Most real-world Erlang applications are built using Erlang/OTP. OTP is set of Erlang libraries and design principles providing middleware to develop these systems. It includes its own distributed database, applications to interface towards other languages, debugging and release handling tools.
As an LFE programmer, you will have the ability and freedom to utilise Erlang and OTP libraries directly from a Lisp syntax.
In order to write LFE scripts, libraries, and applications, you will need to have Erlang installed. There are download links provided on the Erlang site, or you can use a tool such as kerl to download, build, and install multiple versions of Erlang on your system.
The rebar3 site also has a nice intro on getting started quickly with an Erlang installation.