Better Understand the Dock - The Dock (Windows users, think 'toolbar') initially resides at the bottom of the screen with icons that represent the capabilities, documents and storage locations that your Mac may access…
There is a vertical dividing line on the Dock.
Re-Size the Dock by clicking and dragging on the vertical line, up and down
The left side it has applications, the right-side is a place for documents and folders, and storage locations, if they are put there.
Click once on an icon on the left, to launch a program.
To add an item to the dock, click on the document or folder and drag it down to the dock, wait for the icons to move aside, then release.
To remove an item from the dock, click on the icon, drag it away from the dock, wait a second, 'Remove' appears, 'release’. Icon’s gone from the Dock.
To show an item's actual location… Right-click an icon, view the pop-up, select Options > Show Items in Finder.
Accidentally remove it from the dock..? Re-add it to the dock... Go the lower left corner of the screen, click on the Blue Finder icon, select the Applications folder, and select the application, and drag it onto the dock, waiting for Icons to move-aside, then release.
Apple Menu > System Preferences > Dock, provides options to customize your Dock’s behavior.