We know most of the content in a SharePoint page are webparts. If you want to add a new webpart in the page we normally use
Site Actions -> Edit Page
But in some cases the pages are not editable ie you will not find the Edit Page option in Site Actions menu (For example NewForm.aspx). In these cases you will try to edit the page in SharePoint Designer and add a webpart. But if you notice the page you opened in designer it also has a webpart (in our case List Form webpart in NewForm.aspx) in a webpart zone. So why cant we add a webpart to the same zone from the browser. Yes you can! You can get the edit mode of the page by just adding the below name value pair to the query string of the current page.