Word processing properly means formatting any headings using the styles menu, not just by formatting the text. See my post on The 10 Commandments of Word Processing if this is news to you. Once you get into the habit of doing this, many wonderful features become available, like:
Click anywhere in the text you want to make a heading, then choose Heading from the Styles menu, and the formatting/function will update.
Don't like the font? No problem, once you set text as a Heading, change the formatting, then update that style from the menu.
Once you have a document that is using all the Styles you like, you can set these to be your preferred formatting of styles for any Google document that you use.
In the Styles menu, go to Options > Save as my default styles. Now all your new docs will use this formatting.
You can even convert existing docs to this format by choosing 'Use my default styles'.