This chapter has dealt with three extremely powerful patterns that require a lot of practice before using them in production code. It's a very good idea to make some exercises with them by simulating typical production problems:
Create a simple REST server that reuses most of the error-checking and connection functionality to provide an easy-to-use interface to practice the Template pattern
Make a small library that can write to different databases but only in the case that all writes were OK, or delete the newly created writes to practice Memento for example
Write your own language, to make simple things such as answering simple questions like bots usually do so you can practice a bit of the Interpreter pattern
The idea is to practice coding and reread any section until you get comfortable with each pattern.