@yukinoh1989
To go into the period key again:
It’s helpful for zooming in as @hdpeterson said. It also centers the rotation point of the view to the selected object. So if you have trouble rotating around an object, you could use the period key, and it makes rotating around the object much easier.
And it works in edit mode too. Just select a vertex – or a view vertices – and blender now zooms in and rotates around the vertex/vertices. I use it all the time.
