If all goes well during installation you will notice upon starting Grasshopper (GH) that there is a new category called Karamba3D on the component panel. It consists of roughly ten subsections (see fig. 2.1). In case you do not see any icons select “Draw All Components” in Grasshopper's “View”-menu.
The installation can be tested by placing a Karamba3D “License”-component on the canvas: it should not issue a warning or error. If not, see section 4.1.3 for how to solve that issue.