With 4 fours and some operators you have to get the target number below (rose area):
addition: +, subtraction: -, multiplication: *, division: /, open parenthesis: (, close parenthesis: ), decimal point: ., square root: √, factorial: !
Use the green buttons above to create your expression. Your expression will be shown in the yellow area below:
When you are ready you can evaluate your expression or reset the target with the blue buttons below: