Sorry for the delay in response Yvonne.
I would start with Microsoft resources on InfoPath architecture, features, usage, etc.
There are links on the right on the InfoPathDev Home page.
I have found it just takes time experimenting with forms and I have learned more "tinkering". I would recomend always using simple test forms to test and learn about features and understanding there use and then come back and implement them in your solution.
If you are looking to create an enterprise electronic form solution I would recommend you check out the Database Accelerator. It makes your job as a developer much easier by giving you a toolset of out of the box web services to use in your forms.
Qdabra Database Accelerator Suite Version 2.0 - Developer