One of my most popular videos is the above one teaching how to modify an STL file in Fusion 360. There seems to be a high demand of wanting to edit downloaded stl files from Thingiverse or any other file sharing site. Most of you can probably relate. You download a file and need to simply tweak a tiny part to make it fit your application.
Fusion 360 actually makes this pretty simple with the introduction of the Mesh environment and the ability to convert a mesh into a brep. Once converted to a brep, you can then proceed to edit the design as you would any solid.
You do have to be careful however, a file with too many facets (over 10,000) may give you trouble. To see how to address the issue of modifying an stl file with a high number of facets check out this tutorial on Modifying a High Poly STL in Fusion 360.