The other 2 gents have mentioned the winds, and they are a big player--especially on such a long flight...
As you mentioned being a newbie, it might help to to think about the effect of the winds in this way...
Imagine you're at an airport (or other place) that has one of those moving sidewalks, from point-A to point-B, but that it's busted. As you walk along from A-B, you're progressing at a certain speed, with nothing helping nor hindering you. An aircraft flying in similar "still" air (no headwind or tailwind) calls this "true airspeed."
OK, now you're walking that same moving sidewalk from A to B, and it's now working, also moving the same direction A to B. Your feet are still walking the surface of the moving sidewalk at the same speed as they were when the moving sidewalk was busted, but now you have the additional speed of the sidewalk itself moving from A to B. As you look left/right at things that are *not* on the moving sidewalk, you'll see thing going by pretty fast.
Finally, let's assume you're at B wanting to go back to A, but the moving sidewalk is still running in the direction of A to B. As you walk back towards B, your speed on the sidewalk itself will be the same as before, but your overall progress back to A will be slower, since you're "fighting" the A-B movement on your B-A trip. You'll notive things on the side going by much slower.
The effect on a long aircraft trip can be a big one, as mentioned. For example:
Assume a 5000nm trip, a true airspeed of 450 knots, and 100 knots of headwind (or tailwind).
100 Headwind (minus)
350 Groundspeed (GS)
14:17 Time enroute (Distance divided by GS)
000 Wind (Still air)
11:07 Time enroute
100 Tailwind (plus)
09:06 Time enroute
As you can see, the difference is about 5:00 of flight time, and if the aircraft burns fuel at the rough rate of 10,000 pounds per hour, that's a difference of 50,000 pounds of fuel, which may mean that 50,000 pounds of payload (people, baggage, freight, etc.) does't make the flight that has to contend with these kinds of headwinds.
One of the things we (dispatchers) do is to determine flight plan routings that avoid/minimize headwinds, while seeking favorable tailwinds.
Sorry for the length, but I hope this sheds lends some context to the effects of the winds..
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.