I have two kinds of flags. Each flag has a field that gets a value. I want to add these field in one field of views. Any user can flag a content by two kinds of flags.
Should I use "views field view"? What is the instruction?
You may be able to do this with native views.
Using field rewriting in views you can insert values into field display originating from other fields in the same row if they are ordered to appear above it. You can also use a "Global: Custom Text" field and add values and HTML to construct complex output.
Add the fields you want to be displayed as part of the rewritten/global field should be ordered to appear above it by clicking the reorder button and using the handle bars to drag fields up and down.
Those fields you want to merge should be set to exclude from display.
Those hidden fields will be available as a token value you will be able to use elsewhere in the view row in the global custom text field, or combined field.