We learned earlier in the course that "dùng" also means "to use", so are there certain rules when deciding to use "dùng" or "sử dụng", or are they interchangeable?
They are interchangeable.
Oh ok, cảm ơn! ^^
You can also use xài but usually for money.
sử dụng = 使用 Cantonese : sai2 jung6 Mandarin : shǐyòng