This is the start of a really great series. It uses Swift for the examples but everything in the articles holds true for any language/platform
First, some quick terminology:
an error condition is a failed conditional check that results in a function skipping its usual functionality and instead returning an nominated error value.
an error is a value used to report that an error condition occurred and normal functionality was skipped
error handling is code that looks for errors and performs different actions based on the presence of those errors
error reporting communicates an error result from a user task to the user