In this Cinema 4D tutorial, we go through the steps of using a spline with the new Cinema 4D R15 Bevel Tool. It's not as simple as drop and drag a spline into the spline field. First, you have to make sure you are using an open spline and then orient it correctly to use with the Bevel Tool. The only way to get used to using the new spline feature with the Bevel Tool is to play around with it and see what does and does not work.
Don't forget to view my recent series of Cinema 4D Beginner Quick Tips. Ten Tips I wish I knew when I first started using Cinema 4D.