It will be my first time using a whopper plopper. When or what conditions should I throw a whopper plopper? And so what colors? 

1.  Where the water is wet. 
 

2.  Yes. 
 

Honestly, I haven't been overwhelmed by this bait. Caught a few. Bring a popper and try that when the plopper isn't producing. 

I’ve caught them in full sun, total cloud cover and everything in between. Not so much in windy conditions. Seems to do better in calm water. 
 

I mostly cast, let it sit until the ripples disperse and then reel it in back to the boat/bank. But, you can twitch it and work it like a popper.  Move it about 8”-10” and it will “plop” about three times. 

What these guys said.  Keep in mind the ONLY color that matters is the BOTTOM of the lure.  The fish can't see the color on top.  The WP and the Choppo can be a great lure in my area sometimes...sometimes not, just like any other topwater. The best tips I can offer for it are:

1. Throw it at pinch points or when you're seeing some surface activity

2. Don't use braid. 

3. Like @BrianMDTXsaid, let it land, let it sit for a couple seconds, start reeling.  If you've made a long cast you'll want to start with the rod tip low and gradually raise the rod tip as you're reeling to keep the nose of the WP in the sweet spot as it gets closer to the boat.

 

I know some people don't care for them.  It's usually the first topwater I throw.  Maybe second only to a frog. 

Whopper Plopper 110 or 75 (skip the 90) : Bone , Loon and Monkey Butt will cover your color needs .