Hey,
The clip holds the rounds, the magazine, wether integral with the rifle or detachable traps, the clip which prevents it from entering the magazine proper. The thumb is then used to press down on the rounds forcing them into the magazine where they remain. The stripper clip is then manually withdrawn or automatically falls away- depending on weapon design. This is basically the method of charging a wepon/magazine with fresh rounds. Next question, should be: "how does the clip on the M-1 rifle work"? Stay tuned!