=if(A1=TRUE,"TEXT","")
When you say "...if a check box on [a] sheet 1 has been selected" do you mean if the check box has been ticked ?
If yes, then it is fairly straightforward to use a formula that refers to the cell link for the check box.
For example, let's say the check box uses cell A1 as its cell link.
Code:=if(A1=TRUE,"TEXT","")
This will show the word "TEXT" if the check box has been ticked, and will be blank if the check box is unticked.