When making any flower you start with the centre and leave it to dry hard to provide a stable base for the creation. For the poppies the centre is the seed head. This is made using some pale green flower paste. Either buy the paste coloured or colour it yourself by adding a small amount of green food colouring paste and kneading it through to an even shade. Take a 24 gauge wire and use some pliers to bend a small hook onto the end.
A tiered cake means that the weight of your top tier (or tiers if you're getting extravagant) rests on the bottom tier. To prevent everything sinking into the cake and ruining your beatifully smooth icing, you need to put in some dowels. These can be foodsafe wood or plastic and are available, like everything else, from cakecraft shops or the internet.