The lock symbol on a sketch means it is fully constrained (this is preferable). Also – you should take care of warnings in the timeline.
When trying to fully define a sketch you can use dimensions or what Fusion 360?
When you are applying your constraints and dimensions, your final goal is to fully define the sketch. This means that the sketch is completely fixed. Fusion 360 indicates this by turning sketch geometry from blue to black.
What does fully constrained mean?
Modifying objects. Undoing and redoing sketching actions. If geometry is controlled such that you cannot change it without redefining the relationships—changing constraints, dimensions, or parameters—the geometry is fully constrained.
How do you duplicate a body in Fusion 360?
Copy Bodies in Fusion 360
Fusion 360 bodies can be copied similarly to sketches. To copy, right-click on a Body in the Browser and select “copy.” You can also select the body in the Browser to use the keyboard shortcuts CTRL + C (Windows) or CMD + C (Mac).