You can see sample student submissions, and how College Board scored those submissions, here: http://apcentral.collegeboard.com/apc/public/exam/exam_information/231726.html#anchor3
This Q&A may be useful as well: https://secure-media.collegeboard.org/digitalServices/pdf/ap/create-student-performance-q-and-a.pdf
The Create Task is very open ended, students can make anything they want as long as they can answer the written questions about their program. Students should be able to describe the purpose of their program, develop an algorithm in their program and explain how it works, and develop an abstraction in their program and explain how it works.
The program needs to be complicated enough to the point where students must break the problem down into sub problems, develop algorithms to solve the subproblems, and develop an abstraction to manage complexity (the abstraction in most submissions will almost always be a function that takes in parameters, and the function should be called multiple times as part of the solution).
Coming out of the CodeHS AP CSP course, we expect several student submissions to be games, choose your own adventure stories with text based input and text based output, choose your own adventure stories with text based input and graphical output, tools that do some useful computation for the user, or image filters. The Create Task must be a program, not a website.
Students can develop their Create Performance Task in the Performance Task unit of the course, or in the CodeHS Sandbox, but will need to upload their final submission to the College Board AP Digital Portfolio.