In the libgdx wiki, this particle editor is recommended. And this blog was helpful. But the problem is that I am not sure yet how to use it for my game. Let's say I want to have a fire-effect in my game. How can I get help for this particle editor?
Found the answer in here. You can directly use the output of the editor in the API. It's really cool.
If you mean 3D particle effects, there is also a "new" Wiki page for using the particles: https://github.com/libgdx/libgdx/wiki/3D-Particle-Effects