The difference between the Japanese 7 "shichi" and "nana" and 4 "shi" and "yon"?

Are they used differently in different situations? I umed "nana" and "yon" were used for 7 and 4 when used in conjunction with another number (like 17 "juu nana" or 64 "rokujuu yon"), but I'm not sure. Could I please have that clarified?