You can mix coins by sending to a address with a mininum deposit of 0.01 BTC.
Bitmixer take a fee of 0.0005 BTC + 2% Fee + Selectable Fee (more security).
BitMixer will send from another input address your bitcoins where you entered at the first step.
That means nobody know where your BTC will be forwarded. It takes a lot of time to trace your address back.
You will receive a Code for the next mix. That is useful if you won't get the bitcoins what you sent earlier.
Like I read before, Bitmixer is a Mixing Service. You can invest in Bitmixer if you're holding 100 BTC or more in your wallet.
level6
Salmen explains bitmixer very just above.
I have used their BTC mixing service many times now, even though I am no whale. I do not want my BTC origins to be obvious, I also want to be reasonably experienced in using their service. I have never had a real problem with bitmixer, the one complication I did have was resolved just fine.
I was impressed enough by their service to join their Signature Campaign.
If you want to use their service, follow their instructions carefully!