How to print a document made with A4 pages to A3 pages back and front in the style of a booklet

There is the Print Booklet feature to use if you are physically connected to the printer. The Pages in your document must be single pages and you must have a mumber of pages divisible by 4 (since folding an A3 in half will give you 4 pages A4). The Pages in InDesign are kept in reading order starting with a single right page, the reading order is seen in the Print Booklet dialogue. (One way to start is to follow a tutorial like this one https://www.youtube.com/watch?v=oAAJD69Ns0I)

If you do not have the printer connected so that you can use the "Print" command then you need an imposed PDF, this can be done by placing the original Indesign document placing all pages in an indesign document, but there are specialised software for this both as PDF plugins and stand alone applications, as well as parts of RIP workflows such as Fiery, but it many be an option you do not have. A PDF document can also be printed as booklet from Acrobat, again provided the page number is divisible by 4. (As mentioned in other posts if you are expecting edge to edge printing you will need to print on oversize A3 or SRA3 / A3+  size, with more complexity also comes more complexity of explanation.) There are different solutions depending on your demands, if it was not a specialised field there would not also be specialised solutions… but it is possible to do it manually if you have a cool head (and a dummy to help you keep things organised)

BookMaker and/or Imposition Studio from Devalipi.com are good options for this if this is somethnig you do regularly. With this software you can also compensate for creep and it allows for calculations of more complex binding. These software are trya and buy… I don't rememeber if you get full feature limited to a week, or watermark on trial.

I'm happy to talk more once I better understand your needs. If you ontop of this are planning to separate the colors of this booklet, like if you are printing on Riso, again this adds complexity and you would need a couple of days training and perhapps help to setup a workflow. This is beyond what can be answered in this type of forum.

Is nice that she/he is asking for how to print in a booklet in A3 and all it got was "are you sure you have a A3 printer?". Gosh. Still looking for an answer too. 

Is your desk-top printer A3 or A3 +? If the former, you won't be able to have bleeding images? You'll have to experiment to see how you can best arrange the printing of the facing pages on to the A3 sheet and also to successfully duplex the printing. Maybe fiddly!

If you're just printing this to an office printer, you can stick with A4 in single pages (the better way to do it, by the way) and instead of using File>Print, do File>Print Booklet. Your printer must be able to print A3, but I'm guessing you have that already. If you're asking how to send this to someone else to do the same, your best bet is to save as PDF (still in single A4 pages), and tell them to use Acrobat's booklet feature.