Your device is identified by the name you’ve given it with an option to make it ring. Click through the search result (you will be asked to sign in again) and you will see options for making the device ring, to lock it, and to erase it.
The ring and location feature will help you find your phone if you’ve left it some place or if you’ve just misplaced it at home between books or it’s fallen into the sofa. When your device rings, you can silence it by pressing the sleep/wake button. Your phone must be connected to the internet. It doesn’t necessarily need to have a SIM card inserted in it but it does need an internet connection. And because I can’t quite help myself I have to point out that iOS did have this feature before Android did.