Let you know:让你知道……

例句:

我们一得出结论，我就会让你知道。

I will let you know about it as soon as we come to any conclusion

我们一得出结论，我就告诉你。

Ⅰ will tell you about it as soon as we come to any conclusion.

tell you:

告诉你如何做;对你说;告诉你;

例句:

Any high school student could tell you the answer.随便一个高中生都可以告诉你答案。