Either you will make a petition to the court, or someone else will petition to make you bankrupt. If someone else has asked for you to be made bankrupt, you’ll be made aware of it by the court. If you don’t want to be made bankrupt you’ll need to prove that you don’t owe the person applying for money, or you’ll need to pay back any money you do owe them.
The first stages of the bankruptcy process are usually managed by an official receiver, who works for the Insolvency Service. They are normally your trustee unless an insolvency practitioner takes on that role. Your trustee explains the bankruptcy process to you and sells any goods or assets that you own which are not everyday household items or things needed to do your job.