Roll out your marzipan on a clean dry surface dusted with icing sugar (in exactly the same way you would roll out biscuit dough etc.) to about 5mm thick- as always the exact thickness can vary with preference, but try to make sure it's even :)
Take about a tablespoon of apricot jam and heat it in the microwave until it;s just bubbling. Push it through a seive to remove any lumps and allow the runnier part of the jam to cool. When it's a little cooler brush the jam all over your cake- like pasting wallpaper paste over a wall to help the paper stick.