The top one is a Bundle function. It creates clusters from any type of input. The bottom is a Build Array function. It creates an array from the same type of element. These are both explained in the LabVIEW help. The top method is used when you want a single XY Graph. In this case you wire in an array of X values and an array of Y values to get a cluster of two arrays. The bottom method is used when you need multiple XY curves on the same graph. In this case you get an array of clusters.
I would
strongly recommend that you go though the LabVIEW tutorial. As I indicated, there's examples that ship with LabVIEW that show the various graphs.