If it just started raining and you still have dry wood you'll want to start your fire quickly. Use a lean-to style to keep your tinder dry while you light it, and slowly add the driest kindling you have. Move your dry wood under the vehicle or put it under a tarp while it's raining. Don't worry about the rain putting your fire out. If you're actively keeping the fire going, the rain won't put it out unless it's a downpour. Keeping a fire going in the rain is much easier than starting a fire with wet wood. Read more tips for camping in the rain here.