please explain this in English, thanks.

Before I answer your question here, I'd like you to tell me what fixed costs are and what variable costs are. This topic here will be taught in out Microeconomics next term.

Example of Opportunity Cost
Q: Suppose you have a free ticket to a concert by Band A. The ticket has no resale value. On the night of the concert your next-best alternative entertainment is a performance by Band B for which the tickets cost $40. You like Band B and would usually be willing to pay $50 for a ticket to see them. What is the opportunity cost of using your free ticket and seeing Band A?
A: The benefit you forgo (that is, the value to you) is the benefit of seeing Band B. As well as the gross benefit of $50 for seeing Band B, you also forgo the actual $40 of cost, so the net benefit you forgo is $10. So, the opportunity cost of seeing Band A is $10.

Capital
For economists, capital includes all manufactured aids used in producing consumer goods and services. Included are all factory, storage, transportation, and distribution facilities, as well as tools and machinery.
Capital used by economists refers no to money but to tools, machinery, and other productive equipment. Because money produces nothing, economists do not include it as an economic resource. Money is simply a means for purchasing goods and services, including capital goods.

Tina has $5,000 to invest. She can invest the $5,000 in a certificate of deposit that earns 5% annually, for a first-year return of $250. Alternatively, she can pay off an auto loan on her car, which carries an interest rate of 7%. If she pays off the auto loan, she will save $350 (7% of $5,000) in interest expense.
Question: What is Tina’s opportunity cost from investing in the certificate of deposit?