Chances are you've had at least some experience using effects. If not, get ready for some fun.
Reason's effects sound processors can animate your instruments in many ways: They can add realism or incongruity, enhance or reduce quality, distance sounds or bring them to the fore, and even distort or add speech effects.
It's a good idea to get your tracks sounding their best without effects first, especially if you plan on using a lot of tracks. Effects that sound great with a few tracks can become a burden as you add more.
However, this is not always possible. Sometimes you'll choose to build a song around a particular effect. This does not have to be a problemjust keep in mind that you may need fewer (or sparser) parts as a result.