how do you write 4 to the power of soemthing using microsoft word.

Write 4 X 4 X 4 X 4 X 4 as a power of 4.
I know the answer is 4 to the power of 5.

I just don't know how to write it using microsoft word?

What you want to write is 45.

In Microsoft Word, you would write 45. Then go back to highlight the number 5. Go to the format menu, submenu fonts (with the big "A" letter). A Choice panel will appear and somewhere in the lower half, you should see "effects" with a checkbox called Superscript. Check the checkbox and click the "OK" button. You should have the superscript for the number 5.
Different version of Microsoft Word could vary in the details.