Networking concept and spawning questions

Hi everybody

First, i'm a frenchy guy and my english is not perfect.

After doing a tutorial on Unet (a simple multiplayer FPS that i succefully managed to work), I got some difficulties to understand the way unity run scripts when you are in configuration of a host server with a local client and some remote clients as we can easily do with the unity's network manager.

When i start my game and choose to be the host, unity start the server and create a local client. At this time, if i understand correctly, there is one and only scene shared by the server and the local client ? and if i run (in a script) a function with [Server] attribute that instantiate and spawn a prefab, how the instantiate method can create the gameobject only on the server if there is one scene before spawing the prefab on the network ? (i see that the gameobject is not active until spawning) i'm a bit lost with the "server" and the "local client" behaviour ...

Can anyone try to explain me how a script is executed in a case like this ?

Thanks for your awnsers !