you can find a couple ways to buy the plugins from here
As for the capx, how you display the ads is up to you.
I have 2 different ways:
1) i have a global variable named GameOver and each time the player dies 1 is added to that GV. When the GV is equal to random(7,9) i show an add.
2) in my store i have a reward button. When the player clicks on the button an ad displays, and they are rewarded with 3 of my power-ups.
Now, for the way I add the cranberrygame plugin to Intel XDK:
I need to mention this 1st > everytime i go to build i delete the previous build. I have had a few problems if i kept an old build in the Intel XDK projects list. It may just be operator error (my fault) but i hate wasting my time. It makes for a few extra steps, but saves me headaches in the long run.
Exporting from C2 - uncheck minify script > make sure use new Intel XDK project format is checked.
After opening Intel XDk - in the lower left hand corner click on open an Intel XDK project
When the project is opening I always have an error box pop up telling me that the cranberrygame-plugin-game-variable is missing. No worries. Just remove and keep going. I will add it later.
After the project is open - click on Plugin Management. Again, I have had problems with leaving 3rd party plugins as they are. So i delete any plugins i am using in my C2 project (i only use 3 for now).
Click on Add Plugins to this Project > Third Party Plugins
Moving from top to bottom:
click on git repo (1st arrow)
Click inside box Repo URL (2nd arrow) > copy/paste > https://github.com/cranberrygame/cordova-plugin-ad-admob.git
Click on Plugin Variables - Enter the required value (3rd arrow) This is where you will enter your AdMob ad unit ID you entered in your C2 project.
Click Add Plugin and you're done. And always make sure Test Mode is set to Yes in AdMob properties in C2 when you are only testing.
Switch it to No when you go live.
*Forgot to mention, I am using the latest version of Intel XDK 3759