You need to learn about the WP concept of Templates and Themes. Themes are how pages are “built” and styled, and take content from the WP database as the page is
Templates are part of Themes, and describe how a page specific page is built.
The database is where all content is stored, including Media (pictures, etc). Each post/page/media item is an entry in the database. A theme will pull data from the database, and format it with the CSS/etc that is contained in the theme.
Since you are new at WP, then the best place to start is the WP Codex. There are lessons there. Plus any number of places to learn how WP works. The Codex starts here: https://codex.wordpress.org/ .
Dreamweaver is a web server (and a editor), which processes HTML-like code (and HTML/CSS/etc) to build a page. It can include content from a database, depending on how the site is built.
Since the client/employer wants to convert a site to WP, you will need to find a theme that you like, modify the theme, then manually create the content (WP posts/pages/etc). A bit of work; it will be like creating a brand new site. You can’t directly ‘import’ between DW and WP.
So, start with the Codex (and other sources – tons of them via the googles) to learn how WP works. Find a theme you like (which can be a real time sink), modify it for your need (through Customization screens, or perhaps a Child Theme), and start copy/paste your content. Big project. But can be done.
Added after your comment:
If you need to put some content in the sidebar, those are called ‘widgets’. You will need to write some custom code that will display whatever you want according to some conditions (page content = something, or day of week = something).
You probably need to start with some knowledge of the Widget API (here https://codex.wordpress.org/Widgets_API ). Then you can create a widget that contains your custom code to output things into the widget’s area on the sidebar.