CC rainfall not working

What layer are you using for the rain effect? What layer are you dragging it onto?

Here's a link to the CC (Cycore) effects manual.

You can find some tutorials on the Cycore Website

I would probably add a black solid to the comp, apply CC Rainfall to the black solid, adjust the settings until I got the speed and look I think I want, then set the layer's blend mode to Screen or Add to finalize the effect. I usually also end up adding some additional color correction to the layer. Just applying CC Rainfall to some footage limits the ways you can blend the rain into the shot. As with most composites, it is often a very good idea to use multiple layers and stack them up with blend modes and mattes or track mattes. I've used CC rain to make it rain outside a window, or behind people walking under an awning by using multiple layers and track mattes.

If I get a minute later this evening I will post a screenshot of how I would set up a typical rainfall composite.