How is Robinson Crusoe and Friday's relationship symbolic of imperialist ideology?
I assume your question refers to the relationship between Crusoe and Friday and have edited your question accordingly...
When Great Britain ruled its extensive empire, it did so with the understanding that British ways were superior to all others and that part of the purpose of empire was to bear the "white man's burden" of civilizing the natives.
A reader can see Crusoe exhibiting this same sort of attitude towards Friday. He values Friday because Friday seems more "British" than the "savages." He refuses to try to learn anything from Friday, refusing, for example, to try Friday's methods for making a canoe.
Crusoe treats Friday as an inferior who is valuable to the extent that he can act British. This is symbolic of imperialist ideology.