what is the different between * and IP core multiplier

I assume by IP core you mean "lpm_mult"?

Using lpm_mult you have more control over the multiplier unit to be target. Typing '*' into your code you are at the mercy of what the synthesis engine picks for you. So for portable coding '*' is a better approach but when you are tuning your design for performance or area you might need to resort to using lpm_mult. I recommend using '*' and when that doesn't give you the results you are looking for then try replacing it with an instantiation of lpm_mult.