how do I save an InDesign template so it shows up when I open an new file?

A one line script can do it—you can give a script any key command from Keyboard Shortcuts

//Opens a template named MyTemplate.indt—replace with path to your .indt file
app.open(File("~/Desktop/MyTemplate.indt"));

Does it not show in the Recent Files list on the Home Screen when you open InDesign?

You can also define and save a preset (just page dimensions with margins, columns, bleeds etc. but not styles and other useful stuff yiou can save in a template) from the new document dialog.

Hi Phil,

Are you asking if you can set things up so that when you open a new file (File > New) it automatically opens your template, the answer is no. But if you create a template--create a file and save it as .indt--when you open that file, it will open a new untitled document based on the template. I hope that makes sense.