smfshop item to give membergroup

[Plasmaa]

So basically i want to make a SA shop item that gives a certain membergroup (that gives access to a board). I want a warning that gives them an option to go back if they wouldn't want to have access to the board, and 2 buttons one titled "Yes" and the other "No", if the user chooses the option yes it gives them the membergroup, and if the user choose the option no it sends them back to the homepage.

Heres what i have so far(only the very basic warning text),

Code Select Expand

function onUse()
{
return '<strong>The Spam Forum section is a place with very little rules compared to normal forum rules. Its a place where trolls thrive and create drama.<br> If you do not want to be viciously attacked by people who have nothing better to do, turn back now.<br><br><style="text-align= center;"> Are you sure you want to continue?</style>'
}


Also if you could explain what you did or what i should do so i can learn i would really appreciate it.