Label don't change value when I choose one CheckBox

Hello for everyone I am new here,sorry if this post doens't match with at all with how should be,because It's my first post this.

I am wanting to change the value of the Label when I choose one CheckBox,but It's seems that the Label just changes when I click in the Label. I was looking for see if the Label had some Events for make work it but I didn't found one. The Label it's in another groupBox,It's seems like that :

In one GroupBox has 3 CheckBox and i want that when i choosing one or all from that CheckBox will change the value of the Label in the another GroupBox.

Please guys,help me here,I am really wanting to understand why It's not working.