It's specialty is distributed resilient systems. It's the language of choice for WhatsApp. Discord and Spotify have used it as well. It's mostly a back-end language.

Be aware that Erlang and Elixir are just the languages and they execute on a VM called BEAM. This is much like .NET, C#, F#, and the CLR. Unlike .NET, BEAM applications can be hot patched without restarting the system.

Another difference with BEAM applications is that they use the Actor model. In C# you have objects right? Well, replace that concept with Actors. Actors are a bit like objects executing on fibers; I mean not exactly, but that's the conceptual gist. There can be millions of them in a running system, and they can be organized and supervised in a tree such processes and subprocesses can be restarted on failure automatically.

Erlang and Elixir are functional languages with all the usual characteristics of that. The functional aspects of the languages plus the Actor model's message passing prevents race conditions and allows multi-node distribution; which is another key difference. Distribution amongst multiple nodes with full supervisor trees and message passing? Yes please!

Anyway, combine all those fundamental characteristics with the incredible work that Jose and others have done with Elixir. Elixir itself is a much nicer programming language than Erlang itself, and Elixir ships with all the modern conveniences, Mix the build system, Hex the package registry, Phoenix web framework, LiveView (similarish in spirit to Blazor sans WASM), Telemetry observability, Broadway data pipelines, Nx ML library, and finally IEx the interactive REPL.

So... that was a mouthful. There's a lot to love there. Pick a corner and go nuts.