And another way of explaining...
Q1: In a jet, fuel flow is proportional to thrust. In S&L flight, thrust = drag. So min drag speed is equal to minimum consumption rate of fuel, which is a good speed for endurance.
Best range speed combines minimising fuel flow but also covering the ground at a reasonable speed, with minimum kg/hr fuel and maximum nm/hr. Since on the drag curve there is one value of thrust for each speed in S&L, best range speed occurs at only one value of minimum (kg/hr divided by nm/hr). If in school you were ever taught that the gradient of a line = "rise over run", you will see why the minimum gradient line represents minimum FF/TAS, just touching the drag curve at one point.
Long answer to a short question. Hope it helps.