A guarantor is a name given to someone by whom it is pledged that a loan or other type of debt will be paid. Usually, a guarantor agrees that he or she will pay or perform another person’s debt or duty if that person fails to do so. Most commonly the term is used in reference to financial assistance. 
Using Guarantor doesn’t mean that loan will be approved
It does not mean that if a guarantor is used by you than a loan application will go through, due to the reason that the guarantor is considered part of the loan application, and along with the other applicants his or her credit will also be evaluated. If it is felt by the lending institution that the guarantor cannot make good on the debt, then loan will not be approved by them. So when looking for a guarantor, then you should keep this in mind.