Let's say you send out plating of a product part. You form something and send it out for plating. Then when you get it back you assemble the unit.
Now - what is the requirement?
The requirement is that you address the operation as you would any other for the most part. For example it will be on your process flow chart (or the flow chart will reference it in some way).
Basically you apply 4.1 c) "c) Determine criteria and methods needed to ensure that both the operation and control of these processes are effective."
This may include defined receiving inspection criteria - these are things you have to decide.
Now, in 4.1 it is stated: "Where a company chooses to outsource any process that affects product conformity with requirements, the company shall ensure control over such processes. Control of such outsourced processes shall be identified within the quality management system." From your question I think you may be having trouble defining what a 'QMS' ( quality management system) is.
Your QMS can be illustrated in a number of ways. One way to think of it is as a standard fishbone. If you look at your business as a set of processes and inter-relate them this is not all that hard. The important part is ensuring you are clear about inputs and outputs and intra / inter-system communications.
Remember - if you are looking at a sub-contracted process, you are still responsible for determining critical characteristics and such. While you send the item out for sub-processing (for example plating), it is still a process step and is subject to QMS requirements.
Communications channels are represented in procedures. Management reviews, for example, are communication conduits. Staff meetings are conduits. Shift meetings are conduits. This should be only an issue of being ready to discuss the issue and to be ready with specific examples. Remember - communication with suppliers is as important as communication with customer and internal communication.