Why do I have an inflation destination and a public address in my stellarport account.
How can I tell if I've received any staking rewards?
An inflation destination is the account that you're voting to receive a slice of inflation when the newly created lumens gets distributed on the network. See more on inflation here.
If you receive any inflation (either by you voting for your account and/or others voting for your account), you'll receive it on a weekly basis as part of the Inflation operation. In other words, you'll receive lumens in your account.