Hi Waseem Akram,

Searching the text string across the object and across the field will be done by using SOSL. This is Salesforce Object Search Language. It has capability of searching a particular string across the multiple object.
SOSL statements evaluate to a list of sObjects, where each list contains the search results for a particular sObject type. The result lists are always returned in the same order as they were specified in the SOSL query.

  I can give you code sample please go through it and try to implement your requirement.

 
Visual force page:

public class theController {

   String searchText;
   List<Lead> results;

   public String getSearchText() {
      return searchText;
   }

   public void setSearchText(String s) {
      searchText = s;
   }

   public List<Lead> getResults() {
      return results;
   }

   public PageReference doSearch() {
      results = (List<Lead>)[FIND :searchText RETURNING Lead(Name, Email, Phone)][0];
      return null;
   }

}

Controller
 

<apex:page controller="theController">
   <apex:form >
      <apex:pageBlock mode="edit" id="block">
         <apex:pageBlockSection >
            <apex:pageBlockSectionItem >
               <apex:outputLabel for="searchText">Search Text</apex:outputLabel>
               <apex:panelGroup >
                  <apex:inputText id="searchText" value="{!searchText}"/>
                  <apex:commandButton value="Go!" action="{!doSearch}" 
                                      rerender="block" status="status"/>
               </apex:panelGroup>
            </apex:pageBlockSectionItem>
        </apex:pageBlockSection>
        <apex:actionStatus id="status" startText="requesting..."/>
        <apex:pageBlockSection title="Results" id="results" columns="1">
           <apex:pageBlockTable value="{!results}" var="l" 
                               rendered="{!NOT(ISNULL(results))}">
              <apex:column value="{!l.name}"/>
              <apex:column value="{!l.email}"/>
              <apex:column value="{!l.phone}"/>
           </apex:pageBlockTable>
        </apex:pageBlockSection>
      </apex:pageBlock>
   </apex:form>
</apex:page>

If the answer helped you, mark it as solved.

Thank you