need help / advice on setting up my DW CC2017 website

1. Take it my 1st step is to define website?

      Yes.  And add your web server's FTP log-in credentials and root directory. Contact your web host for details.

2. I want to create a website to suit all screen sizes, so do I use bootstrap to make my template and all other pages thereafter?

     Yes, you could use Bootstrap.  But you need to understand HTML &  CSS classes and have a working knowledge of how Bootstrap's 12-box grid system works.

• Bootstrap 3 Tutorial

3. Since there are 3 screen sizes - when I create my page using the larger size, do I save each page 3 times (with same page title) and do I then end up with 3 of every page in the right H/S column under website?

  No.  One web site is all you need.  But it must be built responsively to work on various screen sizes xs, sm, md, lg.

4.I haven't a clue about html - I just enter a table with the 4 or 6 columns across - in the editable region and enter images in them with some text - will this still work in CC2017?

     No.  Tables are not responsive.   And if you don't know anything about HTML, you have some homework to do before you can build a website in Dreamweaver.

• HTML Tutorial
• CSS Tutorial

Nancy