How To Write Ten To The Second Power(10 Square) in ms word or other documents ?

There are actually two ways to do this. The easy way is to select the 2 and 

press Ctrl+Shift+=, which is the keyboard shortcut for Superscript. Or you 

can press Ctrl+D to open the Font dialog and check the Superscript box.

Alternatively, you can use the Unicode character 00B2. You can either open 

the Insert | Symbol dialog and insert it (find it in the Latin-1 character 

subset) or type 00B2 and then press Alt+X.