When I choose two checkbox one change the value of the other

So guys, I am new in C# and I am doing Course of Programming(professional programmer),but as I am new to this language of programming,I am kind of lost in some parts. Please if you guys can help me, I will thanks.

I choose two CheckBox and the Label doens't get the two values to do one result. One changes another.

Example :

I choose CheckBox1 and CheckBox2 but just one of the two CheckBox will return the value to the Label1. I want to make it the Label1(result) gets the two values or more values to put together in one result. How can I do that ?