If you have received a copy of an Application for divorce, this means your spouse has applied for a divorce and you have been served. In a sole application, your spouse (who filed the application) is known as the applicant and you (as the other party) are known as the respondent.
You should read the application as soon as possible and acknowledge you have been served. If you do not agree with the facts in the application for divorce, or you oppose the application and do not want the divorce granted you may file (and serve) a Response to divorce.
See Divorce: I have been served for more information.