Well the prof should have given you a time frame by which he would contact you again. Your inability to explain your research might not slice the chances of your selection if your dicipline requires less of public interactions example chemistry, mathematics etc. I think it would be good to inquire him about the position if you did not hear back from him within 10 days. You might be the first candidate he had interviewed and he might be waiting to interview more before he makes the final decision. If your position was an advertised position the prof might have received plenty of qualified applications and wanted to interview several. While, if you have applied for regular admission and you have been interviewed your chances are pretty high. I have been in several selection committees and usually not more than 3 are interviewed in the latter case. Good luck.