First, you need to setup the camera on your WiFi network. This usually involves installing an app on your phone, then following the instructions (usually involves pressing some buttons on the camera, choosing the correct WiFi, typing your WiFi password in the app, etc.)
Once this is done, you should be able to see the camera while on your home network. You should then try to see the camera outside your home network. If you don't, you may want to enable "upnp" in the router's admin interface, or forward a specific port, but that's usually unnecessary.
I hope this helps. If you need any more details, please provide more information about your setup, the steps you've tried, etc.