If your skin is quite dry then use Undercoat under both the Kalme Day Defence and/or Chameleon Concealer and Night Cream. If it's not dry, then only use it under the Day Cream/Concealer.
Always wear undercoat under any make up put directly onto your skin. So if say you are going out in the evening and applying new make up without the Day Cream, then always apply Undercoat first before your cosmetics.
When using under other products apply Undercoat first after cleansing and wait a few minutes before applying other products.