The chart is written in a key-agnostic way.
Select your key and click any of the chord names in any of the boxes to see what each chord resolves to in the specified key.
The blue squares (down the center) have chords that are in the currently selected key. These are your primary chords! The green squares (on the edges) may or may not be in key, but can be used occasionally to create depth/tension, etc.

you may find some of the other links on this site helpful

Mike, I posted this maybe 8 or 9 years ago. I have a copy always in my songwriting notebooks. It’s one of the best tools for writing consonant chord progressions that exists, in my opinion.

I just reposted a similar and simpler chord map that mostly consists of what you see as blue squares in this post in the Songwriters forum:

Writing Melodies - For the Creativity Challenged