The difference is concerned with how parameters are passed to a function. With call by reference, any parameters passed refer to the actual variable, whereas with call by value the parameters refer to the VALUE of the variable, not the variable itself. Consider the following example:
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int mainProgram()
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int x = 3;
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addOne (x);
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return x;
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End
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void addOne(int x)
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x = x + 1;
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End
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If this programming language uses pass by value by default, mainProgram will return 3, because addOne doesn't affect the original value of x.
However, if it uses pass by reference, mainProgram will return 4 (as addOne incremented the variable, not just the value).
Hope this helps. (If not, hopefully someone else will be able to explain it to you better)
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