Federalism is evident in the issues of this case because the case concerns the extent to which the federal government can impose its laws on the states when state laws are in conflict with federal laws.
Our system of federalism is one in which the Constitution gives some powers to the federal government and reserves others to the states. These powers are not always clearly defined and so there can be conflicts over which level of government should be in control of a certain area of law. This is the issue in this case.
The state of Oregon passed a law allowing physician-assisted suicide. The law was in tension with the Controlled Substances Act, a federal law. The issue, then, was whether the federal government could prevent doctors in Oregon from acting in ways that the Oregon law allowed them to act. The Court decided that the federal government could not prevent doctors in Oregon from performing assisted suicides. It ruled that the drugs in question were not illegal under the Controlled Substances Act and therefore that the federal government could not tell the states how doctors could use those legal drugs.
This case is connected to federalism, then, because it deals with the respective powers of the federal government and the state governments.