Erlang Solutions distribute optimisted builds of the Erlang/OTP packages via the link above. These packages are available for a variety of operating systems, including (but not limited to) Ubuntu, Windows, Mac OS X, Fedora and Debian. Follow the instructions at the download page to install.
Most *n*x-based operating systems have pre-built Erlang/OTP distributions in their package management systems (e.g. homebrew on OS X).
To obtain the source and build Erlang/OTP for yourself, see the Ericsson Erlang download page.
Since every Erlang application you work on will require you write source files, you’ll need a way to work sanely with them. The most commonly recommended IDE for writing Erlang is emacs: it has a very feature-rich integration with a wide array of tools and utilities for working with Erlang.
Less common, but viable, options available to you include: vim (using the vimerl plugin) and erlide (based on eclipse). Of course, you are welcome to use any text editor you wish, but you may find toolchain integration less complete with options.
For a great guide to your first steps into Erlang, head on over to TryErlang for an in-browser, interactive tutorial to help you get to grips with the basic syntax and mechanisms of the language.
Once you’ve started to get a feel for the mechanisms available to you in Erlang, head on over to Learn You Some Erlang. Open a terminal and fire up erlang (by running `erl`) as you read through the site. Running through the examples on the site, as you read through the explanations, is one of the best ways to learn Erlang.
Once you’ve started to get to grips with the more complex and glorious features of Erlang and OTP, pick up a copy of Erlang Programming for reference. You might also be interested in learning about rebar: a tool from Basho (the guys behind Riak). They have provided a great guide to getting started with it on the rebar wiki.
Getting involved in the Erlang community is a great way to both improve your own skills and techniques and encourage the others you interact with to improve theirs. A great place to start is the erlang-questions mailing list, or by perusing the unanswered questions on stackoverflow.com. You can also try our very own forums here at ErlangCentral.org. If purely electronic interaction doesn’t quite cut it for you, there are also the Erlang Factory events.
For some more advanced testing techniques, you might wish to check out PropEr: an OSS property-based testing tool. If you’re looking for something more commercial with full support, you should also look at QuviQ’s QuickCheck.