"The Foam"

When we got our Personal Vapors (PV) it came with a battery, atomizer (atty) and cartridge (cart). The battery is what gives the atomizer the energy to "heat" up the coil inside while taking up the ejuice from the cart. The cart is filled with ejuice (whether it was filled from the vendor or from us dripping our own ejuice into it). The ejuice is held in the cart by the foam.  

You will see the white foam in the black cart. When vaping with different ejuices it is best to clean them between different flavors so you don't mixed the flavors, although, sometimes mixing flavors can taste nice.

But after a while the foam will just become yucky. So make your way down to a pet store (PetSmart) and buy yourself  a box of FLUVAL filters used for fish tanks. The one I bought was the 3 pack and good for 104-205 filters. It costed me $3.70 for amount to last me 10 years (joking but it's plenty). Replace your foam often to keep it clean and fresh.