This is the simplest type of assignment and most of the defaults can be safely accepted. You should find that the assignment is already set up to work with a simple 1-100 scale.
You must pay particular attention to your opening, closing and post dates.
Discourage the students from using graphics at the beginning of the document. Turnitin is designed for processing essays. Turnitin may fail to process a document with elaborate graphics at the beginning as it will not be recognised as a textual document.
University software does not recognise the .pages format. Valid formats for student essays are .doc, .docx, .rtf, .odt, .pdf
You may wish to accept PowerPoints through Turnitin so that you can use the Turnitin marking tools, but a similarity check may not be particularly meaningful; consider switching it off in such cases.
For a full tour of the Turnitin settings, watch this video.
To view a demonstration of creating a rubric and attaching it to the assignment, watch the above video, starting at 6.33 on the timeline.