How do you convert Daily Interest Amount into an Interest Rate?

Divide the daily interest rate $$ by the loan balance - that gives you the daily interest rate...then multiply that by 365 which will be your annual rate. This works assuming that your daily interest amount in dollars steadily decreases (on a month to month basis assuming you make payments).

When you trade currencies you are really swapping bonds. The idea is that if you go long EUR wrt USD then you are borrowing USD buying EUR and depositing the EUR proceeds in a a risk-free interest bearing account. The proble is that there are two rates here - a borrowing rate and a lending rate. The essentially risk-free rate that is available to big FX markets participants at which they can lend and borrow money is called the repo rate (the repo rate is the rate you get by borrowing money using a treasury bond as collateral). Thus, the difference in the rates implied by forward pricing is called the implied repo rate.