An IVA is a formal agreement between you and your creditors, managed by a licensed Insolvency Practitioner (IP). Your IP assesses your income and essential outgoings, then proposes a monthly payment you can realistically afford. If your creditors holding 75% or more of the total debt value approve the arrangement, it becomes legally binding on all of them.
A typical IVA lasts five to six years. During that time, you make a single monthly payment that gets distributed among your creditors. At the end of the arrangement, any remaining debt included in the IVA is written off. You can include most unsecured debts: credit cards, personal loans, catalogue debts, overdrafts and some tax debts.
For more on how IVAs work in practice, StepChange has a detailed IVA guide worth reading.