One of the problems I, and many other beginners, had when coming to Squeak was in building a GUI for my application. There are many half-built and unmaintained GUI builders out there, but most of the core Squeak applications are built manually using SystemWindow. Although these are thought of as self-documenting, I found it difficult to see the wood for the trees when examining them.
My first experiment was to build a simple Image-viewer application, which demonstrates how to build a SystemWindow-based application, how to access the file system and how to interact with the user.
It's packaged up as a Monticello package. If this is not something you've used before, have a look at the Wiki notes page, which gives full instructions on how to download using Monticello.