There are 5 total parts in the Amazon interview loop (more on that here) and behavioral interview questions are part of every single one.
No matter what you do to prep- spend the lion share of your effort preparing for this section.
During the behavioral interview, you will often be asked questions that start with "Tell me about a time when..." or "When was the last time that...". Amazon has designed the process to focus on you giving real examples of a time that you've experienced something at work.