Rob Booker is a forex seminar entertainer, a forex "systems" marketer and he is not a successful trader. I can say this from plenty of personal experience: I attended two of his seminars, co-taught another one with him in Canada, and am mentioned in his book. Once Rob held a contest to see who could submit the most profitable system. A guy wrote an elaborate description of a "winning system" and submitted it, knowing full well that it was a system that was a guaranteed loser. Rob awarded him first place, lol, and never tested the system! Rob makes nearly all of his (big) money from selling systems-of-the-month (stuff you can easily find online.) He has not been seen on FF since professional trader Phil McGrew (look him up here--his posts are gold) made him his "buddy" and would speak the truth whenever Rob would post. Stay far away from this clown.
An investor can profit from the difference between two interest rates in two different economies by buying the currency with the higher interest rate and shorting the currency with the lower interest rate. Prior to the 2008 financial crisis, it was very common to short the Japanese yen (JPY) and buy British pounds (GBP) because the interest rate differential was very large. This strategy is sometimes referred to as a "carry trade."