Are you printing yourself, or sending it out to a commercial printer? What's your OS (this actually matters if you need to impose for printing and you don't have a duplexing printer [one that prints two-sided])?
I know there's a built-in Print Booklet feature, but honestly I've never worked with it. I think the InBooklet plugin that shipped with older versions of InDesign did a pretty good job, but I don't have any experience with this newer one. Maybe somebody else here can speak to that.
To get a handle on imposition -- which pages match up with which so your finished booklet will assemble correctly -- you might want to start with making and marking up a dummy of your booklet.
For a booklet that will be 12 pages when finshed, take three pages of paper and fold them together so you have a booklet (without the staples). Number the pages starting with the front cover, all the way through to the back cover - you might also want to sketch out what content is going on each of these pages while you have the dummy assembled like this. Then take it apart to see how the pages need to go together to work in the finished booklet. Notice that your front and back covers are on the same side of the same sheet; the back cover is on the left side of the spread. On the other side of that sheet, you'll have page 2 on the left side, with the inside back cover on the right.
When I do small projects like this, I typically set up the InDesign file to the finished booklet size (8-1/2 x 5-1/2, portrait), and work with the pages in standard order, 1-12 for the example above. When everything's as complete/correct as it's gonna be, I PDF it, then set up another document to the size of the paper I'm printing on (8-1/2 x 11, landscape), and place the PDFs into each spread for the correct imposition. PDF that, and those are the printer spreads that go to my printer.
There are undoubtedly easier ways, and you might take a look at the Print Booklet feature and see if that gets you where you want to go without all the steps above, but this has worked for me for the small booklets I've printed over the past several years.
Mary, there are free scripts for simple impostions, and the IDImposer plugin is free until the end of the year. There's just no justification at all, in my mind, for doing that sort of manual imposition. Overview | IDImposer
See, I knew if I posted something, someone would come up with a better way...
Thanks for the pointer to the plugin. I do this type of job so infrequently and the jobs are so small that I haven't bothered looking into other options, but it's good to know about that for the next time.
Pick it up now. After the new year it goes back to regular price (still pretty reasonable if you need it).