vector - Adobe Illustrator: How to create a clipping mask

I have this logo I am working on. I have 2 questions:

1) I have a white circle behind the 4. I'd like to use that circle as a clipping mask for the 4 so that the 4 fits perfectly within that white circle. How can I do this?

2) After that, if I wanted to paint the 5 areas in white (between blue and green) each a different color, how can I isolate those areas to paint?

Thanks!

Answer

For a clipping mask, grab the circle and bring it to the front, select it and the 4, right click and choose create clipping mask.