Hope I don't sound like too much of a jerk but that's a malformed question and if you need to ask it you probably have a lot of research to do before you make your first successful knife.
You should add the type of knife ypu want to make and the type of steel you are using to your question in order to get a good answer.
In general a wood fire won't be hot enough. You need to get the steel up to at least 800 degrees celsius or hotter.
You can heat treat a simple steel like 1075 or 1084 with some charcoal, a hairdryer, a length of steel pipe, a hole in the ground, and some vegetable oil.