Not sure how to "activate" this.

Have you downloaded the zenpage package and installed it according to its directions?

If so, you will see it in on the plugins tab. Check its box like you would for any other plugin.

But of course, if you are not using a theme that already has support for zenpage you will not see anything until you modify your theme to use it.

Using default theme "adapted" so will look for the link to download. Falling behind ZP