you need same roms in pc and vita
for example i have nes roms in windows at C:/nes_roms/ this i write to right down place and hit read folder. now you see list of roms. in vita i have roms in data/nes_roms/ this i write to top left place then select core from list for nes i use fceumm_libreto.self and under select system name I select "Nintendo - Nintendo Entertainment System.lpl" and hit create wait and save with name "Nintendo - Nintendo Entertainment System.lpl"
sample picture from app and opened "Nintendo - Nintendo Entertainment System.lpl" file in notepad++
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