Stations are build from a core and several modules. In combat, you can target the modules with "R", but you can't target the core. The problem is that to target the modules, you first have to know where they are, which is far from obvious. Stations are designed to look homogeneous, after all. Targeting the core does nothing, so if a player doesn't yet know about the way stations work, that can be very confusing. Saw that confusion in some YT let's plays.
So my idea is: Targeting the core switches through targeting the modules. Hover the cursor over the station core and press "R" once to target the first module, press it again to target the second module and so on. Ideally, the outline of the now targeted module would flash briefly.
This could help you to initially understand the structure of the station and later to identify any left-over modules.