I want to create some code with MiniSnap in NX but the SNAP_Getting_Started_10 does not explain how to create sketches and handle them. I want to encapsulate 2D geometry in sketches. Where can I get more detailed information about this.
SNAP doesn't have functions for creating Sketches, though it has a good selection of functions for creating 2D and 3D curves, which might do what you want. Look at Snap.Create.Line, Snap.Create.Arc, etc.
MiniSnap is a (free) subset of SNAP. It's really only intended to allow you to work through the tutorial examples in the Getting Started guide, so it's intentionally quite limited.
All the SNAP functions are documented in the SNAP Reference Guide (the CHM document), often with example code. In general, if you can't find a function in that document, then it doesn't exist.