With the old reddit design, you can create your own Multireddits. If you switch to old reddit (click username dropdown > "Visit Old Reddit"), and hover over the "Join" button on a subreddit, you should get a menu to check and add that sub to a multireddit (or create a new one). Some subs with custom CSS break this functionality, but this is a way to curate and categorize your subs. So you can read posts from all of you favorite programming-related subs together in one multi and all your favorite cooking ones in another, etc. Once you have them set up you can use them in the new redesign, but to manage them you need to go back to Old Reddit.