Imagine bank notes had a public past, meaning every transaction that was ever made with a note was visible.
In this example, would you accept a note, knowing that it may had been involved within a criminal activity in the past?
This tiny example shows a general issue of Bitcoin. It's the lack of fungibility, how this feature is called. Fungibility allows you to accept and use values, because you don't know details about their use in the past. This is a feature we're used to and that bank notes naturally have by design, but Bitcoin lacks this property.
As soon as you provide personal details, for example when you buy new Bitcoins, your privacy is compromised. In fact, all Bitcoin transactions are stored on every (!) computer that participates at the Bitcoin network. It's easy to link your transaction data and build a detailed profile about you. For bank notes however, no such public storage exists. Why should this feature be limited to bank notes, if it is possible to also have it with Bitcoins?
That's where Bitcoin Mixers come into play. By periodically mixing your coins, you can treat Bitcoins just as you would deal with real bank notes. All security measures and your privacy, as well as the privacy of previous users is preserved and restored - easy and fast.
At the beginning, you send a certain amount of Bitcoins that you want to mix to a specific Bitcoin address that is presented to you as soon as you create a new mix. This is explained in detail at the tutorial section.
As soon as the Bitcoins arrive at FoxMixer, they instantly go into a huge Bitcoin pool. This pool makes up the base of a Bitcoin Mixer. After a certain amount of time that you can set freely, FoxMixer picks a random new set of independent Bitcoins out of this pool for you. This set of Bitcoins is then returned back to a single address or multiple addresses owned by you, such that you have full control about how to use it. We don't keep logs about transactions and the details of a mix are deleted automatically after 7 days.