[Jan Olligs]

As far as I know, it is not possible to sketch in assemblies, but you can sketch a new part that is automatically integrated into the assembly.
What I would suggest you to do, is to click on Help>Tutorials. The totorials that come with Autodesk are really good and tell you how to make adaptive parts (as in your second question) and intelligent parts.
Just play a bit with it and try out all the features, that will help you really well in understanding the program.