The term "original interest" is not standard; it is likely you mean simple interest.
Simple interest is calculated only on the initial principal amount. The interest earned each period remains constant.
Compound interest is calculated on the initial principal and also on the accumulated interest from previous periods. This means interest earns interest, leading to faster growth over time.
The key difference is that simple interest only applies to the principal, while compound interest applies to both the principal and any previously earned interest.
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