The following is an except from oracle documentation.
Overview of User Processes
When a user runs an application program (such as a Pro*C program) or an Oracle tool (such as
Enterprise Manager or SQL*Plus), Oracle creates a user process to run the user's application.
As my understand, an user process is a piece of software that can connect to an oracle server. You (the user) can start a piece of this kind of software, then connect to oracle. If so, why Oracle creates a user process to run the user's application?
This text is trying to say that the application starts a client process that can connect to the database. The database manages server processes and background processes; the application runs the client process.