You may need to do what Tigana said, but then click Customise and go through each level of numbering and adjust the indenting so that it doesn't indent - a painful process but hopefully worth it if you're doing a long document!
Your first number will be number position : Left, aligned at : 0
Text position 36pt, indent at 36 (or alter to your preference).
Next, click on Level 2. If you're wanting all your numbers and sub-clauses to be straight down the left margin, just follow the steps above, making sure that the text is aligned at the same position, i.e. 36pt.
If you are wanting bigger gaps between paragraphs, unless you know how to create styles, i would just highlight all the text (ctrl+A) and then click on Format, Paragraph then go to spacing and where it says "After" change the number to 12pt. That should work for you.