This app is for tracking your own Apple devices. Or rather, the devices on which you have configured an Apple ID that you know, usually owned by you or your family (spouse, children...). It is used to locate a Mac, iPhone or iPad when it has been lost or stolen, and act accordingly by locking it, erasing its data or simply beeping to find it.

You cannot track someone else's device, unless you steal it or they voluntarily give you their Apple ID, in which case you are assumed to be someone they trust and they know you can track their phone and don't care.

You can track him as long as you have access to his account. However, keep in mind something very important: the GPS location can always be changed. For example, with Tenorshare iAnyGo, this is very easy to do and requires only a couple of clicks.