^^ Actually, UC transfer applicants have a higher rate of acceptance from CCCs than as freshmen. You are in the correct forum to learn this. UC Transfer students do get financial aid if they qualify.
For the most part, to transfer to UCs you must be a junior standing with a minimum of 60 semester UC transferable coursework toward your major which must be declared (or for some, a pre-major) and GEs such as for IGETC or if for engineering, there may be different GE requirements.
You will have to speak with the CCC transfer advisor with your unique situation of being a high school student too. UC transfer students must complete as many major prereqs prior to transfer so if you are thinking of STEM as a possibility, you will most likely need to finish those prereqs prior to transfer. Many UCs don’t make it easy to change majors once you transfer and some don’t allow changing to a STEM major.