Paragraph styles are your friends.
Make a semantic difference between your paragraphs. Those for the “discourse” should be typed with Text Body (select this style from the leftmost menu in the toolbar). The headings should be typed Heading 1 for first level, Heading 2 for second level …
Once this is done, you can customise Heading 1 to add spacing above and below in the
Indents & Spacing tab of the style definition. Magically, all paragraphed marked Heading 1 will show the increased spacings.
Styles offer so many formatting possibilities that there is no enough space in an answer to address everything. I recommend you read the Writer Guide, especially the chapters on styles.
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