I have finished my medschool and I have also finished 1 year internship

I have finished my medschool and I have also finished 1 year internship at my home country in Asia , will I be eligible to apply for post doctoral research fellowship at US after I finish with Usmle step 1 and 2 ?
Can you please put a light on the eligibility as it’s totally new towards me, are all post doctoral research fellowship paid or not ? What is the duration of this job ?
How can I keep my self updated about newer post doctoral research fellowship jobs , can and IMG from Asia ( Pakistan) be selected for Post doctoral research fellowship in surgery? as my field of interest is surgery …