Look up JBrunner's video about loading 120 reels. 35mm reels work pretty much the same way, though he does it slightly differently from the way I do it.
I do it by starting the film in the center (you don't actually need to clip it, unless it makes it easier for you--if you clip it off center, it will make it harder), and roll the reel on the table about 6 inches at a time, feeding the film in with my right hand, holding the film out parallel to the table surface as I push it onto the reel, stabilizing the reel with my left hand and moving it back to the starting point after rolling it. You should always feel a little play, pushing and pulling on the film.