In this talk, I will give some backgrounds of isoparametric functions (hypersurfaces), especially in the unit sphere. Then I will introduce some applications of isoparametric foliation related with our work, including the first eigenvalues of the minimal isoparametric hypersurface and focal (actually minimal) submanifolds; the Willmore, Einstein, Ricci parallel properties of focal submanifolds, related with Besse's problem; the normal scalar curvature inequality on the focal submaniflds and its equality condition.