The discovery process will list out all the devices it has found and whether or not they are "new" or "changed" nodes. Changed nodes are ones that already exist in Solarwinds. But nothing changes to the nodes until you import them into Solarwinds after the discovery process has completed. When you import them, you can select if you want to import the topology data.
You could however also just go on the particular device and select List Resources for it. And then select the "Topology: Layer 3" and "Topology - Layer 2" options.