There’s a handful of things.
The first things to look for in the manual are custom properties (similar to maya gui layouts, except for some annoying shortcomings when they are created on the fly).
Custom properties can be created and managed on the fly, and be made modal if need be, which is the common way to deal with transient GUIs and control/options panel.
If you need something persistant things are usually registered. In that case the most common way to do it is write a self-installing plugin, which can create, lay out and persist properties.
There are other things like spdls and presets, but they are largely obsolete/legacy for custom gui work other than MRay shaders.
Style wise it’s fairly different from maya. I prefer Maya’s for transient stuff, but for registered/persistant, bar the lack of a colour and vector widget, I prefer XSI.
Conceptually they are mostly callback based ala wx if you want, but without a main event loop (or rather it’s transparent), and with the layout part detached and controllable after composition.
Definitely start from custom properties and self installing plugins in the sdk manual, it should get you started.