What is the "Dash"?

The dash is what you might call Ubuntu's version of the start menu. You can invoke the dash by clicking on the dash icon on the Unity launcher:

or by pressing the Super key (The key with the Windows logo).

This is the dash:

Searching for "disk utilities" should bring up what you're looking for.

See also: What's the right terminology for Unity's UI elements?

For future reference, the Unity Dashboard was discontinued in 2017. If you're running a version of Ubuntu that still uses the Dash, it's time to upgrade.

Ubuntu's Unity Dash served as a user interface for Ubuntu to search for files and applications, listen to music, watch videos, view photos, and monitor online social accounts

Guide to the Ubuntu Unity Dash