Point Clouds created by the DSM tools or by Import are first selected as a whole. That is if you click on a Point Cloud in the 3D View, the whole cloud (all points) will highlight. This means subsequent actions apply to the whole cloud. You can also select a subset of points in a Point Cloud. This can be done with Mesh Edit Mode or if you want to work with an individual point, using the second click method. For example, if you wanted to measure to a specific point in a cloud, you first click on the cloud and it selects and highlights, and then you click a second time on the already-selected cloud and an individual point will be selected (and highlighted with a larger point system for ease of use). Then you can select other points in this cloud (using SHIFT) or in other clouds or other objects to Measure. This sub-point can be used to help set up control points as well.