Hi and welcome!
Did you did the in game tutorials??
This process is explained there. I would advise doing them a couple of times.
By the way, you should patch the game as the process was changed a little after version 1.05 (or was it 1.04?).
It would be no good for you to learnt the obsolete system
About your concrete questions:
1-You need a two star leader commanding a stack and in the influence area of an army HQ stack. Then check the tooltips on the buttons on the left of the panel stack and you will see a light up one to make a corps with him.
2-You need an activated 1* leader. Select him and click on the enable division button on the left of the units panel. Then he will be enabled as a division (his name will be written over a silver band instead of white one). Now you have to put some units on his division.
Select him and with the control key pressed select other brigades, batteries or regiments on the same stack and then press the plus (+) button on the left of the panel. You can add as much as 17 elements per division.
Bear in mind there are three buttons groups on the left of the unit panel. You can switch between them by clicking on the tabs above them.
Regards