I have a website that is built with legacy frames. Its a typical content frame on the left so a person can click on links on the left and open pages in the main frame to the right
in the main target frame of the page.

I have for months been trying to figure out the best way to update my site so I can use newer technologies since regular
frames are going to be deprecated soon. So here are my questions.....

1) I have an accordion Navigation Menu built as a left side NAV DIV. So what should I use to target the main body of the webpage?
Should I use IFrames or is there a way to target a DIV from another DIV?

2) If I am able to click on a contents DIV and have the URL links open in another div on the page what sort of code do I use
to tell the targeted DIV to open that URL based on the hyperlink being clicked on? Here is an example image of what I am trying to do

explanation.jpg