what is the best starting point to prepare for graduate school if you are not well equipped? I suffered seriously from both bipolar disorder and major depression during my undergraduate*. It took me 7.5 years to graduate (including 1.5 year suspended from school due to bipolar disorder), with GPA near 2.0. (Furthermore, I do not fully understand the material in the core courses - approximately 15% of them, mostly last chapters.)

From the day I left school with a bachelor in physics, I have given it carefully thought for literally half year, and determined to pursue a career in physics science. I understand it well what it takes, and what I will face. 

Right now, I am studying statistical physics on my own from John Perskill's open courses on Youtube, I work the problem set and do the reading (and ask questions on Stackexchange), as well as teaching myself a few minor things (such as Mathematica)

So far, my recent priority is building a solid understanding of physics (at least the cores courses in undergrad; ideally even includes quantum field theory.), as well as equipping myself with programming skills, before being fluent in a specific field, then I will be looking for a position of research assistant, and publish research result in 2 or 3 years, such that I have a shot when I apply to American graduate schools (along with maintaining my health). 

My question is: what is the best point to start, given my current situation? 



*Information: I studied in Asia. and would like to do graduate studies in Physics in the States, Japan or Europe.
You might want to take a few courses (at first)
as a special student, a non-degree seeking student.

However, the standards for admission are not less than regular admission invariably.

This is especially true at Ivy League universities 

See my comments regarding being admitted as a
graduate special student at Harvard University I posted on this forum:

https://academia.stackexchange.com/a/61120/123306