You need fury to burst. Build fury spamming corruption, fel flame, and HOG (if not about to burst), and potentially imp swarm. Soul fire if you get procs.
Once you have enough fury to burst (making up a random number, but lets say it takes 700), you want to pop all your cd's, go into form, double chaos wave, and spam touch of chaos.
Demo has lots of nuances and utility (immo aura, demon leap, carrion swarm etc.) that you can learn to use as you go. However, I would work on putting out some damage as mentioned above prior to trying to get into using those abilities well.
I will try to check back if you have any follow up questions.