I assume you are talking about faucets in cryptocurrency?
A bitcoin faucet is a reward system, in the form of a website or app, that dispenses rewards in the form of a satoshi. Faucets can also be found in altcoins and dispensed in there smallest units,
A faucet is a gateway to get cryptos. Not everyone wants to spend money to get cryptos. Faucets allow for a free way to get these cryptos.
Faucets are also a business so faucet make money by putting all types of ads (most do have a restriction on what ads can be shown aka no porngraphic ads)
Some faucet also community donated so they might show less ads, Faucet can be a way for a coin to promote itself.
In fact Nano used faucet to distribute coins. Before it was Nano-it was called Raiblocks can use a simple faucet page to distribute coins .
Faucets can also be a way to get traffic for ones site. That is why 99bitcoins still run a faucet even if they are running at loss.
In fact I will add a faucet to https://bitcointribune.org/
which will be launched soon after the transition to using xopus.
Anyway since I will be adding a faucet to my site-I can tell how they are created.
The easiest way to make a faucet I know is to just one click of a button and have some funds beforehand.
There is a step to step directions to make it:
https://99bitcoins.com/bitcoin-faucet-wordpress-plugin/
Just follow those steps and boom a faucet is born.
The hardest part is that you need initial funds for a faucet to work.