A spell is as simple or complex as you make it. So long as you've studied the basics and understand the principles behind a spell it's relatively simple to create. The basis is building up and releasing energy with an intent all the rest is just to help it along but unnecessary. Most practitioners will use words during a spell and various tools that I'm sure you've heard about but they're to be used at your own discretion. It's all a matter of what works best for you.
Start out with a clear goal in mind and slowly build on it from there, if you feel lost on here to begin look a spell up online and adapt it to suit you best that way you at least get some practice in what sort of things you prefer and can slowly change more and more things until you feel ready to write your own. You may want to look up various things like candle colors and herbs to work in and there is plenty of information on that both in the forums and all over the internet.