Dealing with errors section is a bit confusing

[ramirezfranciscof]

The section on dealing with errors reads a bit confusing to me. At least 2 things stand out:

1. The introduction already introduces a code box but without much context of where this validate would go, which is then also repeated in the following section.
2. At the end when it introduces multiple process handlers it gives 3 examples of how to use it in different subtle ways but does not tell the reader to do anything with these. Perhaps we could rephrase in a more interactive way.

I'm adding this as an issue because I don't think is super critical to have fixed for the upcoming tutorial, but good to keep in mind.