I'm not sure that I understand the numbering format that you want.
Where does the x part come from in your x.y format? If x is a fixed
number, you can use one of the List Number paragraph styles to apply
numbering, and modify it to include a leading "1".

Alternatively, if what you want is a multi-level list, you need to set
up the List Number series of styles as an outline numbered list
according to the instructions in the following article:

How to create numbered headings or outline numbering in your Microsoft
Word document
http://www.shaunakelly.com/word/numbering/OutlineNumbering.html

To apply a numbered paragraph style to text, do the following: Hold
the SHIFT key and click the arrow next to the Style box of the
Formatting toolbar. Scroll down until you find the List Number series,
and pick the appropriate one.

For information about styles, please see:

Tips for understanding Microsoft Word styles
http://www.shaunakelly.com/word/styles/TipsOnStyles.html