You have two ways to add a hotkey in Blender. One is from the right click menu of the operator. Assign shortcut.
This works for quite a few tools. Some tools doesn’t have a assign or change shortcut entry though. And some entries are simply bugged. Like the delete button in object mode in the object menu. Reported since months. No fix yet.
The other method is to do it directly in the keymap editor. This means that you need to know the operator name. The python term, the part behind bpy.ops. . In my example here it’s transform.tosphere
And then you add a new keymap item, and write this term into the upper left field. Which adds the new keymap item. And then you can change the hotkey for it to your needs.
It is sometimes as easy as this. But sometimes there are even more steps involved. Some operators requires you to fill out several fields. You can even call menus with call.menu and the python term for the menu. The new tool shelf is also a special thing. But that’s each another chapter then. I would suggest to read a few entrties in the keymap until you understand the logic behind.
And take care to add the operator in the section where it belongs to. You can break the keymap by adding it in the wrong section. And wrong section can also mean that the hotkey simply does nothing. When it’s a mesh tool that is used in edit mode, then 3d view / Mesh is the right section.
To see the python term in the tooltips activate Python Tooltips in the preferences.