Book and Article Titles
Every project has a Book Details page (Article Details for articles), reached from the top of the chapter list under Front Matter. This is where the title-page information lives.

Each entry here is a variable — a named piece of information that the template drops into the title page, running heads, and the ePub metadata. Which variables appear by default depends on the template you chose; a typical book starts with Title, Short Title, and Author.
Authors and editors
Author is a list, not a single field. Click Add Author for each additional author; use the red × beside a name to remove it. If your template includes editors, an Editor list works the same way, with its own Add Editor button.
The caret beside each name opens that person's detail fields, so a name can carry more than just its display form where the template needs it.
Adding your own variables
Click Add Variable, give it a name, and click Create. The new variable appears in the list with its own text box.
Custom variables are useful for anything the template does not already cover — a series name, a volume number, an ISBN, a dedication, an epigraph. Once defined, a variable can be dropped anywhere in the text with the Insert Variable button on the toolbar — switch on Tools → Boilerplate if you do not see it — or into headers and footers when you edit the header template, so you only have to type the value once.
Removing a variable
Each variable has an X button beside its label. It is disabled while the variable is still used somewhere in the document — hover over it and Inkwell tells you so ("Used in the document — remove it from the document first"). Remove the usages first, then the variable.
Where this information ends up
Everything on this page feeds the built book: the title page as laid out by the template, running heads that reference the short title or author, and the metadata embedded in the ePub so that e-readers and stores show the right title and author.