Duplicate

Duplicate is as simple as it seems. You can duplicate a piece of the mesh and place it somewhere else very quickly.

To use the Duplicate tool:

1. Select one or more vertices, edges, or faces.

2. Press Shift + D.

3. Drag your mouse to move the selection. You can use the X, Y, and Z constraints while moving, just as you would in a normal transform.

4. Left click to confirm.

Duplicate is quite a simple tool, but it gives you a lot of options. For example, from the Operator panel you can control the offset of the duplication, constrain it, and even access the Proportional Editing features.