Once you have created a layout, you have several choices. What you want to do is print or export as a tiled PDF… accessible in the File menu. It will break up the layout into however many sheets the size your printer prefs are set to. Of course you’ll want to make sure your printer is set to A4. Printing will use Seamly to print the pattern. Exporting will allow you to save the PDF, and use the system to print the pattern.
What I highly suggest when tile printing is to include a square pattern piece of known size, like 4 in x 4in so that you can verify your printer settings are correct, and the pattern is printing to scale.