<apex:page standardController="Case" Extensions="CaseHandlerExtn" ShowHeader="False">
<apex:form >
<apex:pageBlock Title="Submit a Case" >
<apex:PageBlockSection Title="Section 1" columns="1">
<apex:PageblockSectionItem >
<apex:outputLabel >Contact Name</apex:outputLabel>
<apex:InputField Id="Id1" value="{!Case.ContactId}"/>
</apex:PageblockSectionItem>
<apex:PageblockSectionItem >
<apex:outputLabel >Email</apex:outputLabel>
<apex:inputField Id="Id2" value="{!Case.ContactEmail}" />
</apex:PageblockSectionItem>
<apex:PageblockSectionItem >
<apex:outputLabel >Subject</apex:outputLabel>
<apex:inputField Id="Id2" value="{!Case.subject}" />
</apex:PageblockSectionItem>
<apex:PageblockSectionItem >
<apex:outputLabel >Description</apex:outputLabel>
<apex:inputField Id="Id2" value="{!Case.Description}" />
</apex:PageblockSectionItem>
</apex:PageBlockSection>
<apex:pageBlockButtons >

<apex:commandButton Id="Cancel" action="{!Cancel}" Value="Cancel" />

</apex:pageBlockButtons>
<apex:pageBlock title="Upload Attachment">
            <apex:inputFile style="width:100%" id="fileToUpload" value="{!fileBody}" filename="{!fileName}" />
            <apex:commandButton value="Upload Attachment" action="{!UploadFile}"/>
            <apex:commandButton Id="save" action="{!Save}" value="Save" />
       </apex:pageBlock>
</apex:pageBlock>
</apex:form>  
</apex:page>

Public Class CaseHandlerExtn {

Public attachment Atchmnt {get;set;}
Public Case Cs{get;set;}
Public Blob Filebody{get;set;}
Public String FileName{get;set;}
Public Id RecId {get;set;}

//Public Contact Con{get;set;}

Public CaseHandlerExtn (Apexpages.StandardController StndCntlr){
      Atchmnt = New attachment();
       RecId = StndCntlr.getRecord().Id; 
      Cs = New Case(status='New',Origin='Web');    
         }
         
 Public Void SaveCase(){
  insert Cs;
  Atchmnt.ParentId=Cs.Id;
  Insert Atchmnt ;
   
  }
  
  public PageReference UploadFile()
    {
        PageReference pr;
        if(fileBody != null && fileName != null)
        {
          Attachment myAttachment  = new Attachment();
          myAttachment.Body = fileBody;
          myAttachment.Name = fileName;
          myAttachment.ParentId = recId;
          insert myAttachment;
           pr = new PageReference('/' + myAttachment.Id);
           pr.setRedirect(true);
           return pr;
        }
        return null;
    }      
}