The user menu is your default tree, and is accessed through the System Administrator role. You can find the Menu item in the screen tree:
The above screenshot illustrates a typical window set-up, which is done as follows:
It is recommended that you define your own windows, or copy from the existing dictionary, for customizations. Because dictionary (system) defined items may be overwritten during the process of migrating to a new version, it is better to copy a window and customize it in the copied window (or create new). This applies to Java code as well: never change the original source as it may be overwritten during migration.