A spirit animal is a guide offering anything you need. Such as advice or help you with a certain spell. Any animal can be your spirit animals like dragons, dogs, cats, or even fish. Any animal you feel well connected to can be your spirit animal.
A way to contact your spirit animal and the most common way is through meditation and dreams. A lot of the time for me at-least my spirit animals comes to be in dreams.
There are a lot of people spreading information about supposed spirit animals which are combinations of many culture's beliefs, cherry-picked to fit a particular paradigm.
Some 'spirit animals' teachings are parts of different Native American beliefs, taught without any connection to that culture, and combined with some European traditions, for example.
A lot of it fits into New Age teachings, and some of it was simply made up.
Some aspects are gleaned from the Golden Compass books, but adapted from fiction into spiritual belief.
Also be wary of those who seem to insist that everyone must have a spirit animal. This is not the case -- not by a long shot. If your attempts to meet your guides -- if you believe in such things -- are not met by visions of an animal, do not be discouraged. Your guide(s) simply may not express themselves that way.
Some guides never reveal themselves, but people believe their guides are with or within them.
There are also traditions which teach that 'spirit guides' and guardian angels are the same, some even suggesting that one's Holy Guardian Angel is an aspect of the self, and not a separate entity.
So please filter everything you read through your own beliefs, and never let anyone tell you that you must have this or that, unless it is part of a specific tradition which you follow.