Most of your development will be done using a web browser and an IDE. I recommend using Eclipse based GGTS IDE. See the first programming assignment about where to download the IDE and it use. You should check your code on the major 4 browsers, IE, Chrome, Firefox, and Safari, both phone and desktop versions. You do not have to get it working on all the browsers, but note what browsers you have tested, which ones it works on and which ones it does not work on.
At mid semester, I will give a lecture on the subtleties of programming on the Grails framework. But you may want to read some about Groovy, Grails and web programming: