"Top of descent" means the point at which you leave cruise altitude.
Flap settings: there is a difference between Airbus and Boeing.
Airbus use small numbers to describe their settings, and have about 3 or 4 flap settings, described as Flap 1, 2, 3 (and 4 if it exists - I can't recall).
Boeing uses different numbers, which vary with model. 737-200adv had Flaps 1, 2, 5, 10, 15, 25, 30, 40. Settings 1 to about 15 could be used for take-off, with the lower settings on longer runways. Normal 2-engined landings would be Flap 30 for low noise & fuel burn; F40 was used many years ago, but is probably not now. A 1-engined landing would be with F15.
B757 & 767 have less settings: 1, 5, 15, 20, 25, 30. Again, lower settings are used for take-off (though my recollection is the 757 uses at least F15 to avoid tail scrapes) and F30 for normal landing, F20 in the 1-engine case.
The use of flap settings through the speed range needs some explanation. Taking the B757/767, the speeds are related to Vref30, an airspeed at which with Flap 30 you are at (I hope I remember correctly) 1.3 times the 1g stall speed. At a typical landing mass this will be around 130kts. Above Vref30 + 80kt you can fly with flaps up; at that speed you select Flap 1 and can fly down to Vref30 + 60 kt; then Flap 5 and down to + 40 kt. This is the usual configuration to acquire the ILS localiser. Then, approaching the glideslope, select gear down, Flap 20, speed back to Vref30 + 20, and finally at about 4 miles to touchdown select Flap 30 and slow to final approach speed - which is not Vref30 but something more which depends on the wind and any gusts, the increment being between 5 and 20 kt.
Hope this helps.