I am now using Twine 2.3.4, and I have no idea what I was using before. It was different, obviously, because all of my projects are generating error messages…
I used to be able to get things to display in a sidebar by creating a “StoryCaption” passage, and that’s not how things work anymore. What should I do instead?
(I have looked at the documentation, and I don’t understand most of it.)
The Twine v2.3.4 application comes with SugarCube v2.29.0 pre-installed, so it is unlikely that you are using v2.1.0 of that story format.
The application can sometimes get confused about which story format (or version of such) to use for a specific project so I suggest trying the following steps first:
1.Open the Twine 2.x application, then the affected project.
2. Open the “Change Story Format” dialog (from the Story Map’s menu) and select any story format other than a SugarCube one.
3. Close the project and the application.
4. Do step 1 again.
5. Open the “Change Story Format” dialog again but this time select the latest version of SugarCube 2.x that you see in the list.
6. Try playing your project.
Let us know If the above doesn’t fix your issue.
Nothing has replaced the StoryCaption passage, it’s still there and should work fine.
You can take a look at the SugarCube “Guide: Code Updates” for information on updating from older versions.
If there’s anything specific you need help with, include the error message and relevant code, and we can help out.
These are the story format options that I’m offered in Twine.
Is there a more up-to-date version of SugarCube that I can find and install somewhere?
My basic question is: How do I start a new Twine story that displays stuff in the sidebar? I created a new story, I added a StoryCaption passage, and nothing I put in the passage is showing up in the sdiebar.
Weird. OK, the current version is SugarCube v2.30.0, see the install instructions here. (If you have trouble getting the file path, just open an empty tab in your browser, drop the “format.js” file onto that, copy that URL from the browser, and paste it into Twine.)
Enjoy! 
Excellent, I will try that. Thanks!
Once you have installed the latest copy of SugarCube 2.x you should revisit the Story Format dialog to make sure the installing of the story format worked, and to change your default story format from Chapbook to SugarCube. Doing these will result in any future project you create defaulting to SugarCube.