Use WordPress with existing site to enable user registration

I manage a small Club site, hosted by GoDaddy, using Website Builder (being a novice appreciate the ease of “drag & drop” development). We were wanting to keep the current site as is, but restrict access to certain pages by Members only. The host does not have the capability of User Registration (Log On) and recommended WP. Looking thru articles on WP.org it appears that’s the way to make it happen. Plan to purchase WP (thru GoDaddy), but first, I’m looking for the Paul Harvey version of how to Import the entire site to a new WP address with a “Member Sign In/Register” block up front, add a registration page, and be able to manage users (fewer than 50).
Once setup on WP, those “private” pages will be removed from the existing site and a “Log On” link added with the WP site URL. Will attack the Blog howto further down the road.
Hope this can be as simple as I’ve attempted to make it..