Add value of (1) to a selected cell or cells
 

I'm comfortable with excel and formulas but never used any of the developer features.

Can anyone tell me how I could:
click a button I have created on the sheet that will change the value of highlighted cells to the value (1) and fill the cells with a color?

In my head this is how it would work:
1) highlight a group of cells
2) Click the button
All highlighted cells would now contain the value 1 and be filled yellow.

I can create the button and assign a macro to it. I just have no idea how to write the macro, or if its even possible.

I'm open to other ideas if I am going about this all wrong.