At the same time, take off some time and read about the Model View Architecture and how to render out put on .gsp pages using a Java framework like Spring. Take an extra look at the controller part of the project though u should look at other parts as well.
PS Remember to also look at how data from the DAO is displayed on these groovy/gsp pages.
Personally i learnt about gsp pages via Java using maven, spring, hibernate with MySQL as my persistence SQL. You can take a look at the openmrs-module-coreapps, you can look at its structure.
As a quicker alternative, you can use YouTube tutorials to create a simple Java Web project with the CRUD operations and use gsp pages to display the output.
I wish u luck