Do you have auto take off enabled? If so, the plane should take off by itself, provided you input throttle. Find this option on your clipboard, options preferences, flight, and check auto takeoff (I think thats where it is).
If you want to take off by yourself, spawn, wait for the engine to get going. If you're flying a single engine a/c, you're going to have torque. This means that you're going to have to apply some opposite rudder, and a little aileron to counter the effects of torque, which makes your aircraft want to go to the left or right. Once your spawn, gently apply throttle. I usually make a slow 5 count from cut throttle to full throttle. As you slowly increase throttle, you will notice your a/c start to vere to the left/right. Apply necessary rudder, and aileron to keep the aircraft balanced and going straight. Once you start to lift off, continue in your gentle climb, and then raise gears. And your off.
Note: People say to also pull back on the stick when first starting to take off, to lock the tail gear, but I don't. I find that it just makes my plane try to prematurely try to lift off, and then stall, but then I'm probably doing it wrong .
Hope this helps.
donkey