How to access API?

I just downloaded bettersnapview, an app used to generate that Window's 7 snap view. It's now asking me for API. Where is it in system preferences?

Edited:

Oh I just realized it's in system preferences - display - enable access for assistive devices....when i googled it
It's strange how that check box is not available in my display
Someone else with Mavericks on google search also said they dont have it in their OS

An API is something programmers use to connect their applications with other services. This sounds like an application error. Can you post a screenshot of the error (Command-Shift-4)?

Here you go but I doubt it.

Screen shot

The assistive devices process has changed in Mavericks which might explain why their suggestion doesn't work. Take a look at this.

(As an aside, I have no idea why they worded this dialog this way. Using programming verbiage is just confusing for non-coders).

I use BetterTouchTool which does the snapping and a lot more, I don't believe I had to enable accessiblity to make this work..

I use Mavericks and it works fine on there..