Where to start
this.domNode = srcRefNode;
The Dijit module _WidgetBase will handle this for you as part of the Dijit life cycle. You can read more about the lifecycle of a widget here.
You will probably also spend a lot of time in the Dojo reference guide. The samples in the reference guide are meant to introduce you to the concepts of the modules and at times may be a little confusing. If I had one wish, it would be to have both DOM attributed and pure code samples for some Dijit stuff.. Then there is the API documentation. The API docs can be a little difficult to navigate depending on your browser, but they do provide the nitty-gritty of what properties/methods are available. I've spent many a sunny afternoon in the dojox/lang/functional docs.
If you're thinking oh man, I don't want to spend a lot of time in docs, I don't know what to tell you. I work with a lot of different libraries, frameworks and languages and docs are the lifeblood of every single one of them. Roll up your sleeves, dig in and find some diamonds.
For more geodev tips and tricks, check out my blog.