Being curious by nature, the first thing I do when I am confronted by a new software is to open each menu and sub menu, then explore each button on the main screen and those in all the dialog windows.
Two important dialog windows to explore are:
Preferences. This one controls parameters that apply to SketchUp whatever the model being worked on.
Model info. This one applies only to the model being worked on.
If you open the Preferences window you see an item labelled “Shortcuts”.
If you open this, you will see a list of all the commands and their associated key used as a shortcut. Scroll the list, there are quite a lot. Notice that, for some commands to become visible in the list, you must in the proper context.
This is where you can change the key associated with a command and add keys or key combinations to the commands that have none.