V-twin means the motor has two cylinders, they are at angles to each other and form a "V
." (degree of angle varies from bike to bike)
Inline Four cylinder machines have four cylinders, all in a line. Some machines have V-fours which have two cylinders on each side of the V.
There are also singles and triples, but they are not as common.
V-twin machines are far more torquie (still not sure if that's a real word) than their Inline-4 counterparts, and cc to cc are not comparable on power. A basic rule of thumb is that a 1000cc V-twin is comparable to a 750cc inline-4, a 750cc v-twin is comparable to a 600cc inline-4 and so-on. I'm quite sure I will be challenged on this since with bike technology where it is, this formula isn't all that accurate anymore. But it's a start.
The question is WHERE does the bike make it's best power? (powerband) V-twins have a lot of power lower in the RPM's while Inline-4's run at their best higher in the revs. Unfortunately again, it's almost impossible to explain, this is something that just needs to be "felt." And I'm sure there are others that can explain the technicalities better than me.
Two strokes you don't really have to worry about unless you're riding a 125cc bike, pocketbike, YSR, some dirtbikes or a rare 250cc racebike.
Two strokes are a whole other can of worms that are quickly becoming extinct.