What is the easiest option to start making instructions? I'd like to make instructions for my kids, which they could read either on paper or on a tablet.

What is the easiest option to achieve that, ideally using open-source software (and running on Linux)?
After testing several software (and figuring out quite a few are not compatible with each other), I tested Leocad, and was able to easily create models and generate instructions.

In Leocad 0.82, going through "Print Preview…" and then printing to PDF generates simple and clean instructions.

http://raphink.github.io/lego_models shows the results I got with that method.