Photon Server unity3d

Hi, I'm new to photon and i'm a bit confused about photon server/cloud. Concerning about unity3d, what's the difference between the client api I use for photon cloud or photon server? TBH I'd like to have something like a photon cloud server running on a local machine when needed. In most of the cases my clients are going to use cloud solution, but in some cases I'd like to run the same software on a local network.

Ps: I'm not talking about a game


Thanks