Welcome!
Microsoft Word 2007
Start by opening the word document you want to ink. Click on Start Inking on the Review ribbon.

A new ribbon, Pens will appear. From here, you can select what type of pen and color you want to use.

Now you can write directly on the document and save your ink annotations. Even if a user doesn't have a Tablet PC, they will be able to open the file and see the annotations.

This works exactly the same way in Excel 2007.