To add special inserts if you are creating your coaster for the first time, you need to tap any node prior to the last one. The editor will not allow you to add special inserts in the last node that was placed. If you have already created the coaster, just tap any node, except the last one, to add your inserts. Note that any special insert will increase the coaster length, so you need to keep an eye to the limit that your current length limit.