multiple cell selection message box

hi guys im looking for message boxes to pop up when certain cells are selected
to make this easier id like the followng

when cell a1 is selected a message box pops up and says hello ( for example )
when cell b1 is selected a message box pops up and says goodbye ( for example )
when cell c1 is selected a message box pops up and says your turn ( for example )
when cell d1 is selected a message box pops up and says game over ( for example )

your help as ever is much appreciated

i dont understand km

its ok i got it thanks km that will do for me