public class ValidUI {
    public String UserName {get; set;}
    public String Password {get; set;}
    public database__c fre{get; set;}
    public PageReference login(){
    if(UserName!=null && Password!=null )
    {
        db= [select User_Name__c,Password__c from Freelancer__c ]
        if(UserName==db.User_Name__c && Password==db.Password__c)
        {
          pagereference ref = new pagereference('https://c.ap1.visual.force.com/apex/ApplicationForm');
               ref.setredirect(true);
        }
         else{

        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO, 'TRY AGAIN... .'));
        return null ;
    }
    }
}

if(UserName==db.User_Name__c && Password==db.Password__c)
{
  pagereference ref = Page.ApplicationForm;
  // ref.getParameters().put('if you want put any page parameter', 'put here');
  ref.setredirect(true);
  return ref;
}