Dock is a section of applications that is seen either in the bottom or sides of the mac desktop, and that is used to open applications directly, rather than to go to folders and open any app. Its just a shortcut zone for applications and also adds to the sleek look of the mac desktop.
When its easy to open applications directly from the dock, you would need to add more applications which you regularly use. And here is a way to add apps to the dock -

Go to the Applications folder in your mac, and then drag any application from there to the dock. This will keep the app in yourapplications folder, and also in your dock.
And not just one, you can drag multiple applications at a time to the
dock. Select them all at once and drag.
This dragging of applications does not delete the app from the applications folder, but just copies the icon to the dock.