A CMS is a website with an admin area where you can manage the website's content (hence the name).
To edit downloaded templates I suggest Notepad++ (a programmer's text editor) or the PHP edition of Netbeans (both free).
Note that a pure HTML template is a bad idea; I'd stick to Wordpress if I were you. Pure HTML means duplicate code, unless it's a one-page website. (Note how the youtube tutorial Avantika linked to clearly mentions you need to make a copy of index.html and save it as contact.html, then change the content. This means a single change in, say, the tag has to be done in multiple documents; this annoyance is precisely the reason why PHP was invented in the first place.)
HTML templates are not superior to a CMS; they are the little brother for situations where PHP or a similar alternative is not available or required.
You can go on this link for more detail:-
