Hi chewybean,
You need to apply to college in order to get an undergraduate degree (bachelors). You are not too late. Many people take time off between high school and college. Your high school grades only matter to the extent of limiting the colleges that you can get into. Another option is going to a community college for 2 years and doing well, then transferring to a 4 year school to finish your degree.
This is a VERY general overview, but I will do my best...
1. Get into college, maintain a good GPA >3.6/3.7 and take the MCAT (also need to do well on this)
2. Participate in extra curricular activities (ECs) that show you have a desire to serve others. You will need a mixture of clinical volunteering, non-clinical volunteering as well as some leadership experiences, and research if you are planning on pursuing an MD. Shadowing is also important, so you can show ADCOMS that you (sorta) know what you are getting yourself into.
3. Form good relationships with your professors who can write you great letters of recommendation (LORs).
4. Continue all of this throughout college.
5. Do not cheat under any circumstances. Try your hardest to not get in trouble (institutional actions, IAs) basically, don't do anything you wouldn't tell your grandma about around the campfire.
6. Do all of the above things well, then apply for medical school via AMCAS (application service to apply to medical schools). You will learn more about this later.
As far as "does my college matter" it is a long standing debate here on SDN (please search some of those threads, you could read about this topic for days). Some say it matters, some say it has no bearings. Just do well in class (good GPA) and knock the MCAT out of the park.
However, like I mentioned in your other post, know that this is a tough road for even the best and most dedicated students. Make sure you are pursuing medicine for the right reasons, because if not, you will likely be very miserable.
You can PM me if I have helped you and you have any more questions
