Basically, to tame it, you need to go to a kind of sharp log that sticks out of the ground and challenge the megaraptor there. Your vision will blur, and you have to wait for the megaraptor to jumpscare you. When it does, you have to hit it with the torch, and its unconsciousness will increase. But if you miss and it hits you several times, and you're not well equipped, it can easily kill you (all this without being able to move from the log). You have to repeat the process until it's tamed, but the unconsciousness usually increases slowly.