Have everything in Feb 1st to be safe. Yes, send high school and college transcripts. For regular freshman applicants you enter classes and grades then send transcripts. For transfer applicants you send transcripts. There is also a transfer thread that is good to follow and ask questions for USC, link is also below. Good luck and Fight On!
http://admission.usc.edu/transfer/prospective/checklist.html
http://talk.collegeconfidential.com/transfer-students/1903737-2017-2018-usc-transfer-p1.html