How can I control my keyboard in C#?

I would like to write a program like in-screen keyboard. I face a problem that I do not know how to output a key to the system which like I am pressing the real keyboard.
I checked System.Windows.Forms.Keys but it seemed to be only handling the pressing event from user but not "pressing" the key by the program itself.
Thank you in advance.

.NET Development16

SendKeys.SendWait("a");
SendKeys.SendWait("{TAB}");

etc

This'll send 'a', wait for it to be processed, and then send a tab, notice the way both are written.

thank you. But how can I find this method in msdn
I am new to programming. I always find difficulty to search such methodin msdn. I was trying to search for Window.Form.Keys. But it seemed to be no information for sending a key.

Find it difficuit myself and then half the time when I found something I still find it hard to understand the formatting, anyway the reason why you didn't find anything is becuase the Sendkeys is not part of the Forms.key class.

Normally I look for description words eg send keys or save file.