By default WordPress native HTML editor present in add new & edit content (posts, pages, CPTs) pages provides you few important HTML tag buttons like bold, italic, b-quote, del, ins, ul, ol, li, code, more, lookup, close tags, proofread, fullscreen. WP Quicktags is a simple and light weight WordPress plugin that adds few more useful HTML tag buttons.
All you will be needing to do is install and activate WP Quicktags and that’s all. Currently this plugin only adds h1,h2,h3,h4,h5,hr,nbsp. May be in its future updates you will be getting more tag buttons.