“Process” is essentially the .xaml file(s) you published. After you publish your project, a package is created that you use in Orchestrator to add/provision the process or .xaml project. A good way to remember is that you are designing a “business process”.
“Robot” is essentially a simulation of a human performing the process. It is pretty much controlling the user id on the machine of your choosing, as a human would. A good way to remember is think of Skynet from Terminator and how the robots are physically doing the things that humans did.
Once you have a Robot added in Orchestrator, it will use those credentials and the computer name of the machine to log in remotely and perform all the tasks in the Job that you run. Therefore, it will run unattended. Note that the user id credentials used must have Remote access or Admin authorization for the machine (seek your local IT support for assistance if it does not).
There are various other things to keep in mind with unattended jobs, but I hope this is helpful.