Your letting agent or landlord could ask your parent or guardian to be a guarantor.
Your guarantor will have to pay the bill if you cause damage or don't pay your rent.
If you have a joint tenancy, your guarantor will usually be signing up to cover all the rent that is not paid and all the damage caused. This can seem unfair as they could end up paying up towards the rent even if you had paid all your share.
The only way round this will be if your guarantor signs a written agreement with the landlord saying that their liability is limited to a specified proportion of the rent (or damage). Many landlords will not agree to this.
Your parent or guardian may want to get legal advice about being a guarantor. They may be able to use legal services available through their home insurance, union or employee benefits.