Chapter 23 is your first port of call for the first. If you’re targeting standard interpreters like Gargoyle and Git then that’ll just work. If you’re wanting to target web-based interpreters like Quixe then there’s a couple of extra conversion steps that the release process doesn’t yet do automatically.
The second question is trickier. There isn’t any multi-choice conversation system built into Inform, so you’ll need to find an extension that suits your needs.
I don’t personally use conversations much in the stories I’ve written, so I don’t have any personal recommendations. Having said that, a quick scan through the repository suggests that one of the following might be worth looking at closer:
Neither of these is a pure choice-menu-based conversation system, though, although they can provide suggestions for supported topics that could be sufficient. Perhaps someone else might have some other suggestions?
Oh, also, regarding the actual display of graphics, you’ll probably want to start with an extension to help with that too (although it can be done purely as shown in Writing With Inform too, and you should read about the basics there first):
Yet another option for dialogue trees is Michael Martin’s quip extensions. Reactable Quips lets you put a list of choices in the middle of a standard ask/tell system; Quip-Based Conversation lets you completely replace ask/tell with dialogue trees. Here are the most up-to-date versions of both: