How do I add my Applications folder to the dock? My apps folder, which was located in the bar on the bottom right of my Macbook Air running Catalina, suddenly disappeared.

How to get it back?
It sounds like you want to restore the Applications folder to it's location on the right side of the dock.


Close any open application windows so that you can see the desktop.
Click once on the desktop and the name in the upper left corner of
the screen (on the menu bar, next to the Apple menu...) says
"Finder" 
Click on the "File" menu and then select "New Finder Window" A window will open up. Depending on your settings it may or may not show what we need to see, which is the side bar. 
If the sidebar is not there select the "View" menu and then "Show Sidebar"
In the sidebar you should see "Applications" 
Drag Applications from the sidebar to the right side of the dock. To the right of the
vertical bar and to the left of the trash. 
Hover there for a second and a space should open up. 
Release the mouse button


Your Applications folder is now back in the dock.