Can I use a power strip and an extension cord interchangeably?

No, you should not use them interchangeably. A power strip has multiple outlets and a built-in circuit breaker to protect against overloads, while an extension cord is just a wire with a single outlet and no protection. Use a power strip for more outlets in one spot and an extension cord to reach a faraway outlet. Never plug a power strip into another power strip or an extension cord into a power strip.