Getting started with ANTLR is pretty easy if you start playing around with some existing grammars and read some introductory material. As you progress, you will want to check out more advanced topics and play around by working with bigger grammars. Also please join us on the antlr-interest mailing list for active discussions on ANTLR and languages.
To get the most out of ANTLR, you should get The Definitive ANTLR Reference. It is required reading to become an advanced user. For example, Part III provides the only thorough explanation available anywhere of ANTLR's LL(*) parsing strategy.
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That should give you a taste of how to run ANTLR on a simple grammar and some clue about how to build a recognizer and translator. From here, you should start with an existing grammar that is similar to your intended application and start modifying it. There are a number of tutorials Tutorials you can look at that explain some of the basics of building translators and provide some grammars to tweak:
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