I want to create water simulation where a drop of water (or some other obstacle) is dropped into a pool of liquid and produces a mountain-like splash that degrades into a smaller and smaller ripples and eventually settles to a glassy water surface.
I have never used Unity before. How hard is this? Are there tutorials that show you how to do this step by step?
This is a rather difficult thing to do unfortunately :( . And it wouldn't be much easier with any engine you use. Here is how I would approach it.
Create a particle emitter that drops particles in the shape of rain drops all over your designated area. Change the ellipsoid box to create a "blanket effect". Add a world particle collider to cause collision calculation with the particles.
Make your water with whatever mesh or plane you want. Add a collider such as a mesh or box collider to it.
Create a script that uses OnParticleCollision() to do the "magic" ripple effect. How you go about doing this ripple effect is up to you. Here is one example that looks great, but requires Unity pro. You could try to do some sort of mesh deformation like this person.