Most of your development will be done using a web browser and an IDE. I recommend using IntelliJ IDEA Ultimate version. See the first programming assignment about where to download the IDE and how to use it. You should check your code on the major browsers: Edge, Chrome, Firefox, and Safari. Test with mobile and desktop versions. You do not have to get it working on all the browsers, but note which browsers you have tested, which browsers it works on and which does not.
There are lectures on the Groovy programming language and the Grails framework that I recommend reading mid semester after completing the programming assignments. But you may want to read additional documentation about Groovy, Grails and web programming while working on the programming assignments:
http://groovy-lang.org/documentation.html
https://developer.mozilla.org/en-US/docs/Learn