If you want to make a block of wood, like you receive as a pinewood derby blank, into a complex shape, there are a few ways you can go about this.
The lowest tech way is to hand carve, using wood carving tools such as chisels and mallets, scrapers, and knives. You'll want some sandpaper in different grits to finish smoothing the shape as you go. Sketch out what you want to achieve on the surface, make rough cuts first with a saw if needed, and then refine using your hand tools.
More info on carving can be found online.
If you want to make something more complex and have access to a CNC cutting machine which can work with wood, you can use that once you have been trained to use it. Most of the machines I've seen only work on one face of the wood at a time, so you would have to make multiple passes to carve out each side as you like.
You will also need to learn and use a 3D modeling software package that is compatible with the CNC machine you are using.
There may be a makerspace or community workshop near you where you can learn more about all of this. Finding a mentor in person will help guide your craft more quickly than reading about it. Try a search online for makerspaces or hackerspaces near you. Here's a map to get you started: https://wiki.hackerspaces.org/List_of_Hacker_Spaces