Eggs in the Pokemon World are a mystery. Of course, this is just the child’s way of the birds and the bees. One real mystery is that the child becomes 100% of one of the parents. Anyway, let’s start with the basics. Eggs are obtained primarily through the Day Care. If you leave two of your Pokemon which are different genders, they will most likely produce an egg. There are some exceptions, like legendaries and some Metal-type Pokemon, which would be very unrealistic if they could create offspring. In addition to leveling, they will produce eggs depending on how the Day-Care Man says they are doing. The levels range from getting along very well to playing separately (not breeding). In Pokemon Black and White, you will be called by the Day-Care Man when he gets an egg. Other versions like HeartGold and SoulSilver have the Day-Care Man call you regarding the egg. When you get an Egg, there are three stages: not close to hatching, semi-close to hatching, and very close to hatching. The kind of offspring will determine the steps taken, and the progress.
For example, Togepi do not need many steps to hatch, and start out at the second stage. Although this is not true for all Pokemon, some hatch very quickly, while some take quite a while. This is recorded in steps. Bulbapedia lists this as cycles and lists how many are needed to get the egg to hatch. Depending on the kind of Pokemon that will hatch, you will have an easy time, or a very difficult time, as crossing bridges and back will only slightly exhaust the steps. I have had Pokemon Eggs hatch, and then one step later, hatch another one. This proves that even Pokemon of the same type will not hatch with the same amount of steps. Serebii calls this Base Egg Steps and provides a value. If you don’t feel like breeding, there are other ways of obtaining eggs, but most encounters are one time only. For example, you can get a Larvesta Egg if you go to Route 18 by the P2 Laboratory. A Treasure Hunter will give you this Egg. I looked up Larvesta, and it takes about 10,000 steps to hatch. (It evolves at level 59, a very long road.) In HeartGold and SoulSilver versions, you get a Togepi Egg, but I forget how. As you can see, it is probably a better option just to breed and then run around with Eggs, preferably your only Pokemon knowing the move Fly.
Since I get Eggs from Route 3, there is no place to run around there. Therefore, I Fly to the Marvelous Bridge located east of Nimbasa City to hatch Eggs. Each time you cross, it takes about 200 steps, slowly ticking the step counter down. There’s nothing like seeing an Egg hatch for the first time (unless you’re used to it because you’re a breeder). It may be a long journey, but it is definitely worth the travelling.