can you explain what is meant here, explain in simpler words?

Explain why an FRA is equivalent to the exchange of a floating rate of interest for a fixed rate of interest? A FRA is an agreement that a certain specified interest rate, R, , will apply to a certain principal, , for a certain specified future time period. Suppose that the rate observed in the market for the future time period at the beginning of the time period proves to ber, . If the FRA is an agreement that r, will apply when the principal is invested, the holder of the FRA can borrow the principal at r., and then invest it at R, .The net cash flow at the end of the period is then an inflow of R,L and an outflow of R, L. If the FRA is an agreement that R, will apply when the principal is borrowed, the holder of the FRA can invest the borrowed principal at r, . The net cash flow at the end of the period is then an inflow of R, L and an outflow ofr ,l. In either case we see that the FRA involves the exchange of a fixed rate of interest on the principal of 1 for a floating rate of interest on the principal