Unfortunately, there is no such thing as a tutorial.

For information on compiling and building, please see doc/guides/compile.md.
For other documentation, please check doc/guides.

For the differences between mruby and CRuby, doc/limitations.md may be helpful.

If mruby is still too large for your embedded device, please try https://github.com/mrubyc/mrubyc.

I think documentation in ruby has always been somewhat of a problem. Perhaps
we can collectively maintain documentation in ruby in a more relaxed way, that
is allowing for more contributors to add content (solely for documentation, NOT
for features). This may need some kind of wiki, I suppose, or a wiki-like infrastructure,
and probably also needs some kind of co-approval. Perhaps github can be of
help here, but I think the first step that may be useful is to get the ruby core team
to understand that documentation should become a LOT better in general. Ruby
works around this by being an extremely elegant programming language, but
documentation-wise I think there is a lot of improvement possible still.

In regards to some of the questions: to me it always felt as if mruby primarily
targeted experienced C developers already, that is people who know C very
well, and also ruby. I think this is a different focus compared to MRI, which
targets more people. Ideally one day we could merge everything together to
not have these differences - would be kind of cool if we could have ruby be a
bit like busybox and lua or the linux kernel, picking what we want to use and
see and omitting the rest.