Cantsay has explained the basics for you. Bitcoin mixers are used by bitcoin users that wants privacy. Let me give you another examples, assuming you have 10 BTC and you want to make use of a decentralized exchange or you want to make an order to purchase something online, these are two examples that can link your 10 BTac to your real identity because the buyer on a decentralized exchange can link it to you, also the seller of what you want to buy online can link the 10 BTC to you. If what you want to buy is 0.05 BTC, you may decide to send 0.055 BTC to a mixer which you will use to exchange to fiat on a decentralized exchange or be used for the purchase of the item you want to order online.

There are two types of mixers:

• Centralized mixers
• Decentralized mixers

On centralized mixers, like https://mixero.io or the Unijoin which this thread is all about, you will have to send the mixer coins and you will be sent a mixed coin which is not connected with the transaction of the coins that you sent the mixer so that your coins can not be traced. But you need to use a reputed mixer because you will first need to send the mixer coins, which the mixer will mix. That is why they are centralized. It is good to use their darknet (.onion) link.

Decentralized mixers are basically coinjoin. Coinjoin means many users to be connected together in a decentralized way the mixer will send their coins to each other in a way that you can not trace or difficult to trace the coins. Just like 50 users to coinjoin 0.01 BTC each in a way that each 0.01 BTC is sent randomly to each 50 users in a way that can not be traced or hard to trace which one is sent to the different address that the coins are sent to for each 50 users. Example is the Whirlpool on Sparrow wallet and Samourai wallet. Or the Jointmarket if you run your own node. Another example is Wasabi but not trusted in privacy again as the company and chain analytic company are spying and censoring coins. All you will do is to use the wallet they are to do the coinjoin and they are noncustodial wallet.

You can see the lists of reputable mixers and their fee on this thread: 2023 List Bitcoin Mixers Bitcoin Tumblers Websites