The alfacast application is independent and you need to install at least two copies of the application. For example: for streaming on first device and for viewing on second.
The devices should be connected to the same network directly, without any network switches, repeaters, etc. If your device is connected in two ways to the same router (for example: WiFi and Ethernet), please use one of the connection methods.
The alfacast application uses UDP unicast/broadcast transmission. There are some UDP broadcast problems with different network routers. Please make sure that your router has correct behaviour with the UDP broadcast protocol.
If you have some problems you can review Router Setup section.