i wrote an article about Dragon Magick that explains it:
now, what do you mean by a 'dragon companion'? Dragons are astral beings, so if you're hoping to get a physical dragon to ride you are sadly mistaken, this isn't real. if you're looking for an astral dragon to teach you, this is possible, but you don't just show up and catch one, or summon a dragon and start ordering it about. [if so, get ready to get burned (depending on the dragon)] if you start studying Dragon Magick, you will one day meet a Dragon Guardian and a Dragon Guide who are there to help you. you are not their masters, they are not yours, you work as equals. another thing, don't assume the first dragon you see is your companion, they will tell you if they are.
a Guardian Dragon is a young dragon about the size of a cat or a puppy who'll live in your home to guard it from negative beings. it's Astral, keep that in mind. your Dragon Guide is an older dragon who typically stays in the astral and is their to teach you and help you on your path. you don't automatically get two dragons the second you decide to study Dragon Magick, it takes years before they reveal themselves. i've studied for about 4 years now, and have yet to meet my guide, only my guardian has come forward. dragons can sense your intend, if you're afraid, or planning on using them for selfish means, they'll know, and they won't help you.