"Because it was scary, I cried."
There's more of a nuance to it, actually. ので places emphasis on whatever precedes it, while から emphasizes the following resulting action or request.
こわかったから、なきました。Because it was scary, I cried.
こわかったので、なきました。I cried because it was scary.
Pro tip: With requests, it is seen as more polite to use ので:
こわいですので、かえりましょうか？(since it's scary, can we go home?) is more polite than こわいですすから、かえりましょうか？(since it's scary, can we go home?)
Placing emphasis on the reason, as opposed to the request, will soften the request, while から will make it seem more demanding, so be aware of your status among those around you and speak accordingly! Being aware if this detail will also help you sound much more natural when speaking :)