Breast enhancers do not stick to the skin, but instead are used in the bra (it is always best if they are given a nice home in a bra, but you can also get great results in corsets and tight fitting wedding dresses).
The bra and the enhancer can work together to give you either a boost upwards, a boost outwards or a combination of the two. The enhancer fills any space out in the bra and then if there is no more room your breasts are encouraged to lift upwards giving you a great cleavage.
Some styles require a bigger cup sized bra to the ones you normally wear due to their size (e.g. style 9 in the larger size can take a 32C to a 32E) but with some sizes you can keep to a smaller bra for more uplift, or a larger cup for a bigger breast profile from the side.