Sora is the product line. It's good basic road kit, and will do most people OK. Its a 9 speed setup (so 9 sprockets at the back wheel).
A double will have 2 chainrings (the "cog" at the front attached to the pedals). It will either be a "standard" with 39 and 52 toothed rings, or a "compact" with 34 and 50 teeth.
The triple will have 3 rings, probably 32/39/52 or something similar.
The fewer teeth on the front ring the easier it will be to pedal (a lower gear) uphill.
The triple makes climbing easier, but it's heavier, shifting can be a bit rougher and maintenance is more fiddly. A standard double will be lighter, much harder to climb with at first and is the choice of the racer (and wannabees).
The compact is a half way house, you gain a lower gear nearly as low as the triple, but keep the lightness/ease of maintenance. The tradeoff is that the gaps between the usable gears will be wider and you'll perhaps find yourself changing gear more often.