get fields dynamically from custom settings or field set salesforce

string query = 'Select ID';
for(Schema.FieldSetMember f :SObjectType.Campaign.FieldSets.SST_CampaignFields.getFields()){
    query = query + ', '+f.getFieldPath();
}
query = query + ' from campaign limit 10';
system.debug('Queury : '+query);
List<Campaign> camp = database.query(query);
system.debug('Queury : '+camp);
for(campaign c : camp){
   system.debug('Queury : '+c);
}

Custom Lookup Using salesforce

Visualforce Page :
---------------------
<apex:page standardController="Campaign" extensions="customApexController"  id="vfassign">
   <apex:form id="mainfrm">      
      <apex:pageBlock id="pb" mode="maindetail" >    
         <apex:outputPanel id="oP" >          
             <apex:actionstatus id="PleaseWait" startText="Please Wait ....."/><br/>          
            <div style="padding-left: 30px;">
               <apex:outputtext value="Select User From Custom Lookup" style="font-weight:bold;"/>
               <input type="hidden" name="newOwn_lkid" id="newOwn_lkid" value="000000000000000"/>
               <input type="hidden" name="newOwn_lkold" id="newOwn_lkold" value="null"/>
               <input type="hidden" name="newOwn_lktp" id="newOwn_lktp" value="StandardUserLookup"/>
               <input type="hidden" name="newOwn_lspf" id="newOwn_lspf" value="0"/>
               <input type="hidden" name="newOwn_lspfsub" id="newOwn_lspfsub" value="0"/>
               <input type="hidden" name="newOwn_mod" id="newOwn_mod" value="0"/>
               <span class="lookupInput">
               <input id="newOwn" maxlength="255" name="newOwn" onchange="getElementByIdCS('newOwn_lkid').value='';getElementByIdCS('newOwn_mod').value='1';getElementByIdCS('newOwn_mod').value='1';" size="20" tabindex="13" type="text"/>
               <a href="javascript:%20openLookup%28%27%2F_ui%2Fcommon%2Fdata%2FLookupPage%3Flkfm%3DeditPage%26lknm%3DnewOwn%26lktp%3D%27%20%2B%20getElementByIdCS%28%27newOwn_lktp%27%29.value%2C670%2C%271%27%2C%27%26lksrch%3D%27%20%2B%20escapeUTF%28getElementByIdCS%28%27newOwn%27%29.value.substring%280%2C%2080%29%29%29"
                  id="newOwn_lkwgt" onclick="setLastMousePosition(event)" title="Owner name">
               <img src="/s.gif" alt="Owner Lookup (New Window)" class="lookupIcon" onblur="this.className = 'lookupIcon';" onfocus="this.className = 'lookupIconOn';" onmouseout="this.className = 'lookupIcon';this.className = 'lookupIcon';"
                  onmouseover="this.className = 'lookupIconOn';this.className = 'lookupIconOn';" title="Owner Lookup (New Window)"/></a>
               </span>
               <apex:inputhidden value="{!txtOwnersName}" id="newOwnerVal"/>
               <apex:commandButton value="Submit" action="{!GetSelected}" onclick="assignOwner();"/>
            </div>
         </apex:outputPanel>
      </apex:pageBlock>
      {!selectedUserName}
   </apex:form>
   <script>
      function checkAll(cb){
          var inputElem = document.getElementsByTagName("input");
          for(var i=0; i<inputElem.length; i++){
              if(inputElem[i].id.indexOf("checkedone")!=-1)
              inputElem[i].checked = cb.checked;
          }
      }    
      function assignOwner(){
          document.getElementById('{!$Component.vfassign:mainfrm:pb:newOwnerVal}').value = document.getElementById('newOwn_lkid').value;
      }  
   </script>
</apex:page>

Apex Controller:
-------------------

public with sharing class customApexController {
    public string txtOwnersName{get;set;}
    public customApexController(ApexPages.StandardController controller) {

    }
    public string selectedUserName {get;set;}
    public void GetSelected(){
        selectedUserName = txtOwnersName;
    }
}