Question: how to apply for visa after getting i20?
Answer: Select your course and university (a SEVP-approved institution) and apply for it.
Get accepted into a school.
Obtain your Form I-20 [or Form DS-2019 (J-1)] from the university.
Pay the SEVIS fee - Pay the SEVIS I-901 fee at least three business days before your visa interview; print a receipt.