So far, what I've learned:
FIORI - SAP Developed SAPUI5 Applications.
It's called SAPUI5 - If you want to develop from scratch. There's a SAPUI5 Reference which seems to be more geared towards HANA, but also gives step-by-step.
First bit of coding
The "Hello World" example is basically an HTML and Javascript combo, which you post into a notepad, then run.
It uses a public version of SAPUI5, i.e. a library stored at sapui5.hana.ondemand.com, rather than the library downloaded into Eclipse.
One way of looking at this is that you've just coded a UI5 app. Another way of looking at it is that you've just cut and pasted into Notepad, depends how competent you're feeling!
Second bit of coding
This requires that you've downloaded Eclipse. This can be done from http://www.eclipse.org/downloads/. I use the "Kepler" version. Eclipse is a development tool totally external to SAP. That's right ABAPers, no more SE80 for you!
You also need to download the SAPUI5 Development Toolkit (SDK) which I got from http://scn.sap.com/community/developer-center/front-end. The instructions there were pretty good, explaining how to tie the SDK to the Eclipse installation.
The second bit of coding is done in Eclipse Proper. You run the wizard and get a View and a Controller created for you. The index.htm ( found in the WebContent folder in Eclipse ) can be run to test the app. But since you've not put anything in yet, it looks empty.
The CreateApp describes using Javascript in the index.html.
Now the sad thing is, on the face of it, this was more work, to achieve less. But what you have done is used the toolkit that you'll use for UI5 development, and dipped your toes in the MVC architecture.
Getting it onto SAP
The guide to getting it on to SAP is here. It describes an upload program, which I didn't need to use in the end. You create an empty BSP, and corresponding SICF node, then go into Eclipse, and share your project as a "SAP UI5 Repository". This bit is really cool, it uses your SAP Logon pad to pick out the systems it could connect to (I used TED). Then asks for your credentials for that system. It then looks at the BSPs available, and asks which one can be looked at.