If you have a large number of items you want to add to your Quick Parts collection, you will probably want to premark the items and take advantage of Pathagoras tools to add the items en masse. Bookmarking the text is the best way to do this.
It is simply much easier to bookmark a large quantity of individual items text and add them with Pathagoras tools than it would be to add the items individually with Quick Parts tools.
You can save the document containing your bookmarks for later use if you want to add more elements and (more importantly) edit existing items. (Remembering exact names of existing Quick Parts is probably the number one frustrator with the Quick Parts tool. Using a saved bookmarked document where everything is visible makes this much easier.
Creating an individual bookmark is easy.
1. Highlight the text your want to bookmark.
2. Add the bookmark by pressing (in the Word toolbar) 'Insert' and then the Bookmark icon. (It looks like a ribbon. Provide a name for your bookmark that is easy to remember and press OK. That's it. to text you want to add to your Quick Part.
3. The bookmark may or may not be visible once you add it. If visible, it will be a set of grey brackets slightly larger than the normal font. If you know the bookmarks exist, but don't see them in your document, make them visible by clicking "File | Options | Advanced | Show Document Content'. Click 'Show Bookmark's and click OK.
If you will be adding a lot of bookmarks, elevate the Bookmark button to your Quick Access Toolbar. That will save you lots of clicks.