How do Torque and HP differ?

I recently made a modification to my Duster. I went to a Chassis Dyno for some test runs. Before the mod at 2,800 RPM I was getting 112.72 HP, not a lot, but my 360 is only slightly modified. After the mod I got 139.99 HP at the same 2,800 RPM. An increase of 27.27 HP There was a slightly bigger increase a lower RPM, on some or the runs, but the dyno operator said that this was the most consistent increase and reliable increase to look at.

Also at 2,800 RPM my torque, without the mod was 207.06. After the mod it was 257.19. An increase of 50.13 Ft Lbs of Torque. The Duster really takes off a hell of a lot faster. I don't have a track nearby to test it on for ET difference, but the operator said the increases could make as much as a 1-2 second difference in ET on a 12-10 second car. Is that accurate?

I was also wondering how HP and Torque differ in moving the car, like if you have a greater increase in HP and less of an increase in Torque, is that better than a greater increase in Torque and less of an increase in HP?

How do Torque and HP differ in their ability to move a car more quickly down the road?

Thanks...