Balance Transfer Questions

I have about 6k of CC debt between the JetBlue Barclays card and my Disney Chase Visa. I am looking to open a Bank of America card with 5% transfer fee and 21 months 0% APR. My question is- how does a balance transfer work? I have never done one before so how do I pay the two cards to get the balance to the BoA card? Do I have to tell BoA what to pay those two cards and they cut me a check? Thanks!