What is a Pokémon? What differentiates it from a normal organism? It's a fair question. At first glance, there doesn't seem to be much that separates a Swallow from a Swellow.

To begin with, all Pokémon are closely related. They have incredibly similar genetic codes. Almost every Pokémon can breed with other types to produce viable offspring, which, themselves, can breed. In most cases, this would result in all Pokémon being classified as one species with a massive variety of subspecies, but laypeople attached the term species to each variety and, for good or for ill, it has stuck. All Pokémon are omnivorous; even those that are almost entirely carnivorous or herbivorous will supplement their usual diet with plants or meat from time to time. And they all enjoy berries, as well as special human-made treats, such as Pokéblocks and Poffins.

Pokémon are quite intelligent. Even the dullest species is capable of understanding more human speech than the most intelligent normal animal. They can comprehend and execute complex strategies in the heat of battle. And, although much more research needs to be done in this area, a few certain species have brains best compared to a supercomputer. There is even the possibility that all Pokémon may be sentient, something which has led to the recent halt of the once common practice of feasting on species such as Farfetch'd.

Last but by no means least, Pokémon are powerful. Magikarp is often ridiculed for being weak, but even this "worthless" species is capable of surprisingly strong tackles and flails. In ancient times, wild Pokémon were capable of destroying whole towns, and it is only through the concerted efforts of the world's best trainers and scientists that we've managed to bring them under as much control as we have. Pokémon can do things no "regular" animal could ever dream of doing. A Starly may not look like much more than a typical bird, but no starling could even begin to create a powerful whirlwind that can blow away creatures that weigh up to a ton. Pokémon can read minds, induce sleep, temporarily enhance their strength and speed, trigger lightning, teleport, change the weather, summon meteors, and fire enormously powerful blasts of energy. And that's not even getting into the "legendary Pokémon."

Of course, this immediately raises a question: if Pokémon are so powerful, and are so numerous and widespread, how has humanity even managed to survive, let alone thrive? And why do such intelligent creatures allow themselves to be "owned" and trained by humans?

Calling the relationship between Pokémon and humans complex is about as much of an understatement as calling the universe big. Entire books have been written on the subject and no doubt more will be written. Professor Samuel Oak, has devoted his entire life to studying Pokémon-human relations, and he'd be the first to tell you that he's barely scratched the surface. Nevertheless, there are some salient points that is summarizable here.

As noted, Pokémon are much more powerful than humans, but on average, we're roughly of the same intelligence. This seems to have acquired us respect from Pokémon, the fact that we were able to evolve this level of intelligence without enormous levels of power to keep us safe (At least, this is what we've been told by several Psychic Pokémon that we've discussed this with). This is also why they're willing to follow and serve us; out of respect. Either consciously or not, they believe that our survival on essentially pure intelligence without equivalent power makes us worthy of being "in charge." This is also why Pokémon are generally more disposed to stay with a smart abusive trainer than a foolish abusive one (though I could make the case that any abusive trainer is a fool).

How is a Pokemon acquired? 

Sadly, far too many people dive head-first into owning Pokémon without doing proper research. 

Among all the other information included, each species is rated by ease of ownership, on a scale from 1 to 10. Ideally, a pokemon trainer should begin with a Pokémon rated 1, 2, or 3. One of these will give little-to-no trouble, even with no experience whatsoever. Having alternatives is advised, in case the first choice is not available.

Call a local Pokémon Center and arrange for an interview. Once the interviewer is satisfied, the interviewee will be asked what kind of Pokémon he or she is interested in. After which he or she will respond with their choices, making sure to mention which is their first choice. Note that if a Pokémon that an inexperienced owner has no business caring for is requested, the potential owner would most likely be asked to leave.

If the Center has any preferred choices, the potential trainer will be escorted to meet them. If not, the Centre will acquire some and will contact the trainer later on. Either way, sooner or later the potential trainer will meet several Pokémon.  After interacting with each one a bit, enough to learn what each one's personality is like, a favourite is chosen. Once that is complete, the trainer fills out a little bit of paperwork, pays a small fee, and then his choice will be placed into a Poké Ball and be handed over. 

If a person plans to use Pokémon primarily for battling, an additional note is in order. It is often recommended that a battling trainer begin with a Grass, Fire, or Water-type, and each region has its own set of traditional "starters" of those three types. The government recommends choosing Grass; a huge pile of leaves causes much less lasting damage to homes than an out of-control blaze or a torrential flood. Once they have obtained their starter, most battling trainers frown on receiving other Pokémon in such an "official" way. They generally prefer to capture them on their own, swap them in trades with fellow trainers, or be given them as rewards for services performed during their travels. For those owners who do not battle, however, may return to the Professor or the Pokémon Center time after time to receive more additions to their household. Unlike cats or dogs, Pokémon can do a very good job looking after themselves, and there is no real "hoarding" problem associated with large amounts of normal pets.

Bear in mind, however, that several Pokémon are very rare and may not be available by such a simple method. There is the possibility of having to hire an experienced Pokémon trainer to journey into the wild and capture one. As these rare Pokémon are typically also very powerful, it is strongly recommended that this step is not taken until a trainer has already raised several more common species and have learned the basic ins-and-outs. Also be advised that some Pokémon have such a bad reputation that once captured, immediate notification and registration with the local government is required.

All credits goes to Thanos6 from fanfiction.net for this guide.