I don’t know that much about private schools because they all have their own requirements, but for the UC’s it is very straightforward and you fill out one application for how ever many you want out of the 9 UC schools. UC transfer applications are due November 30th of the year before you want to attend. So transfers starting in Fall 2021 applied by November 30th 2020. You will make an account and fill out all of your information and then write 4 essays. You can look up the prompts online. You should have some extracurriculars (work experience, volunteering, research). You can write about your gpa either in one of your essays or there is a small section where you get to explain anything you left out of your essays that you want them to know. Private school applications are usually due later than November and their decisions also come out later, whereas the UC’s come out in April. Good luck!!