It means to make an important effect on something,especially a good effect.
意思是对某事产生巨大的影响或者作用,尤其是好的方面.
可以用这个短语：make a big/ a great deal of / a lot of difference
例句:
The fact that I can now organize my own time makes a big difference.
现在我能自己安排时间了,这对我有很大的作用.