You can start to use the MDI forms just by changing the Showwindow property from 0 to -> 1 or 2 depending what you need.
Example showwindow=2 as Top level form this will be the main form and if you want all the forms be considered independent on the windows toolbar you must use everyone as showwindow=2, if you want to create a window inside the main window you must declare this one as showwindow=1 (in Top level Form).
If you are new using forms this will be a little complicated when passing arguments between forms , but if you already did some apps in the traditional way, this won't be so dificult, it depends on what you need to achieve.
Good Luck!