To favourite an article, press the star feature on the top right hand side of the article and it will be saved in the Menu > Favourites section on the left hand side of the app.
You can access this article later for future reading. To remove the article, just click through and deselect the star feature on the article in question.
This function works for both online and offline use, as long as the article is loaded.
(Please note that the app is not synced with the website, so your Reading List articles from the website will not appear in the Favourites section of the app.)