public with sharing class WrapperDemoController {
    
    public List<AccountWrapper> listAccountWrapper {get; set;}
    public List<Account> selectedAccounts{get;set;}

    public WrapperDemoController ()
    {
            listAccountWrapper = new List<AccountWrapper>();
            searchRecord();
    }
    
    public void searchRecord()
    {
        listAccountWrapper.clear();
            for(Account a: [select Id, Name,BillingState, Website, Phone ,Active__c from Account limit 10]) 
            {
                listAccountWrapper.add(new AccountWrapper(a));
            }
    }

    public void processSelected() 
    {
        selectedAccounts = new List<Account>();
        selectedAccounts.clear();
        for(AccountWrapper wrapAccountObj : listAccountWrapper) 
        {
            if(wrapAccountObj.selected == true) 
            {
                selectedAccounts.add(wrapAccountObj.acc);
                // Here you can add the counter or you check the selectedAccounts.size()
            }
        }
    }

    public void ActivateData() 
    {
        for(Account acc : selectedAccounts )
        {
            acc.Active__c ='Yes';
        }
        update selectedAccounts ;
        searchRecord();
    }

    public void DeActivateData() 
    {
        for(Account acc : selectedAccounts )
        {
            acc.Active__c ='No';
        }
        update selectedAccounts ;
        searchRecord();
    }
    


    // This is our wrapper/container class. 
    public class AccountWrapper 
    {
        public Account acc {get; set;}
        public Boolean selected {get; set;}
        public AccountWrapper(Account a) 
        {
            acc = a;
            selected = false;
        }
    }

}

<apex:page controller="WrapperDemoController">
    <script type="text/javascript">
        function selectAllCheckboxes(obj,receivedInputID){
            var inputCheckBox = document.getElementsByTagName("input");
            for(var i=0; i<inputCheckBox.length; i++){
                if(inputCheckBox[i].id.indexOf(receivedInputID)!=-1){
                    inputCheckBox[i].checked = obj.checked;
                }
            }
        }
    </script>
    <apex:form >
        <apex:pageBlock id="PB1">
            <apex:pageBlockButtons >
                <apex:commandButton value="Add to Grid" action="{!processSelected}" rerender="table2,PB2"/>
            </apex:pageBlockButtons>

            <apex:pageblockSection title="All Accounts" collapsible="false" columns="1">
                <apex:pageBlockTable value="{!listAccountWrapper}" var="accWrap" id="table" title="All Accounts">
                    <apex:column >
                        <apex:facet name="header">
                            <apex:inputCheckbox onclick="selectAllCheckboxes(this,'inputId')"/>
                        </apex:facet>
                        <apex:inputCheckbox value="{!accWrap.selected}" id="inputId"/>
                    </apex:column>
                    <apex:column value="{!accWrap.acc.Name}" />
                    <apex:column value="{!accWrap.acc.BillingState}" />
                    <apex:column value="{!accWrap.acc.Phone}" />
                    <apex:column value="{!accWrap.acc.Active__c}" />
                </apex:pageBlockTable>


            </apex:pageblockSection>
        </apex:pageBlock>
        
        <apex:pageBlock id="PB2" >
            <apex:pageBlockButtons >
                <apex:commandButton value="Activate" action="{!ActivateData}" rerender="PB1,PB2"/>
                <apex:commandButton value="DeActivate" action="{!DeActivateData}" rerender="PB1,PB2"/>
            </apex:pageBlockButtons>

                <apex:pageBlockTable value="{!selectedAccounts}" var="c" id="table2" title="Selected Accounts">
                    <apex:column value="{!c.Name}" headerValue="Account Name"/>
                    <apex:column value="{!c.BillingState}" headerValue="Billing State"/>
                    <apex:column value="{!c.Phone}" headerValue="Phone"/>
                    <apex:column value="{!c.Active__c}" headerValue="Active"/>
                </apex:pageBlockTable>
        </apex:pageBlock>

        
    </apex:form>
</apex:page>