The concept behind baking is taking a texture map of a high Polly (HP) model and wrapping it around a low Polly (LP) model creating detail but not doubling the tri-count. This can be done with any two models that are the same, the reason I chose a HP and LP model was because we had to get this done for a test, so it is easier to explain. In other words, you would 'bake' all the textures and apply them to the surface of another model to create a texture.
When creating the barrier & barrel we created both a low tri-count and high tri-count model. This gave us a chance to learn how to bake and then give it a try for ourselves. The involvement of the high Polly model is so that it can be used to create a high definition texture to be wrapped around the low Polly model. This can be done many ways but all end up with the same end product.
(LP barrier failed first version)
The way we done the barrel is explained exactly how we done it, by creating a low-Polly and high-Polly model and wrapping the texture. The barrier on the other hand was a little bit more troublesome. The way we created the barrier was called 're-topology'. The way this works is by taking a high-Polly model, creating a layer around it and drawing on the wire frame/faces ourselves. This did take some time, and yes I did manage to fail at my first attempt (learning curve). The second time I tried to create the correct wire frame it came out perfectly. After creating it we put all the faces together which turned out to be the low-Polly barrier. The images below are of both the HP & LP barriers.
(LP barrier)
(HP barrier)
As you can see, there is a clear difference between the two but one allows for more detail rather than the other. I attempted to put in a good amount of detail on the parts needed, but the bake normally would take over and create most of the detail itself anyway. We then created a 'cage' which in retrospect allowed for a smoother and cleaner bake, is a way of making the render look more clean with hard edges. The way you use a cage is by grabbing the LP model and making it bigger than your original LP which determines how far the rays from automatic UV will cast. It's normally used for control and clean edges, some people find it tedious and unnecessary but for this part we were being taught it in-case it was needed in future reference.
(LP cage)
After doing this your model is ready to be put into a texture program such as substance painter to be properly painted and textured.