These two features both allow you to keep tabs on players that you like, and could potentially add later. 

This is a feature that is available to you during and leading up to your league's draft. 

A queue allows you to create a list of players that you are interested in drafting. In case you cannot be present for your pick, or your timer runs out, the CPU will autopick from your queue. Once your queue is empty, the autopick will take the next best player based on your roster needs.
​
You can access your league's specific draftboard, and at the bottom, you'll see some icons to the right of the players:

If you tap on the purple paper icon, that will add the player to your queue, which is visible in another tab on mobile:

 On the web app, it will appear on the right and will look like this:

You're able to re-order the players, or you can remove them from your queue entirely. Once they are drafted by you or another team, they will automatically be removed from your queue.

In the first photo from above, you may notice the star icon next to the players' names. That represents your watchlist.

This is an option that you can use throughout the year. The watchlist gives you the option to track players that you may or may not own. It's typically used for players that you want to pick up or trade for later on, you'll be able to view these all in one place.

Watchlist is account-wide which means your tracked players will be visible on all leagues, not for each league.

You can find your watchlist on the right side and you'll see your list of players along with a tab for the latest news updates about them:

You can press on the start icon at any time to remove or add a player to your list. You can also add a player to your watchlist by pressing on the star icon right from their player card. 

If I wanted to add Aaron Donald to my watchlist, I can do that by pressing the star icon to the right of his name: