HI,
I can't help with C# but assuming you can make a Hello World addin, you need
to access the Project Application Object thru the Globals collection.
To add tasks, record a macro of you adding a task in Project VBA then
convert the code. Note that Office applications have numerous Parameters
that in C# you will have to provide for (mostly using #missing is it?). In
VBA or VB optional parameters make code much simpler and easier to read.
--
Rod Gill
Microsoft MVP for Project
Author of the only book on Project VBA, see:
http://www.projectvbabook.com