So having more time (in stead of a hasty post from my phone on a break at work), I can elaborate a bit better, too:
There are many different aspects of spirit animals.
Some people believe a spirit animal is merely a representation, while some others believe it is a sort of guide, or even an aspect of the inner self.
Some people believe that someone will have one spirit animal, while some believe a person may have more than one. Some people believe strictly in one, or that however many animals represent different aspects of the person, while some believe in two: one spirit animal, and one 'shadow' animal representing a challenge in the person's life.
Some people claim that they follow "the" Native American tradition regarding spirit animals. This is simply not the case. There are as many different religious teachings of Native Americans as there have been groups. Some belief systems are very strict, while others are very open. Some teach a spirit animal as in a personal animal, while some teach it as a generational representation, and some teach it as basically a mascot. Some teach it as a totem.
Some people believe a spirit animal is permanent; that one 'meets' their spirit animal during their first spiritual experience. Some believe the spirit animal changes as the person develops through life. Some believe that as the person changes, they acquire more animals (I have not heard this last one as often, but I have heard it). Some believe a spirit animal may 'come' to a person during a time when some aspect of the animal is needed, and may depart after its task is finished.
Some people get information mixed together from many different traditions from different Native American groups, European traditions, more recent philosophies, and ore, and lump it all together into something else.
I'm not saying any of this is wrong, or should not be. I am merely demonstrating a bit of the very wide swath of beliefs on the topic.
I do not follow a tradition including spirit animals. But from what I have heard, people most often use pathwalking or some other spiritual journeying to find or meet theirs, if they believe there is one for them.