You can have multiple action bars apart from the ones that are enabled by default. You can also further increase the amount of action bars and adjust their positioning via add-ons (Bartender is a very popular one and lots of packages like ElvUI have action bar customization).
Also while there are no key bindings on additional bars per default, you can add them in your key bindings menu.
Regarding your question:
Is this the "correct" use for those slots?
There is no "wrong" or "right" way to use your action bars. But there are certain things that will make performing well in combat easier.
If you want to completely optimize your gameplay you should aim for mapping every single slot in your action bars to a keybind (yes that would be about 100 or so key-binds). This can be achieved by using modifiers (Ctrl, shift, alt) and mouse buttons in addition to normal keys.
Don't worry though, it takes some time to develop a system of key-bindings that is right for you and you shouldn't rush it.
During the time you still have unbound slots you should prioritize between two things: Out-of-combat (mounts, food, teleports) and combat (damage, CC, utility, cooldowns) skills/items.
You should aim to have as many combat skills as possible placed in slots with key bindings.
For out of combat items or skills it doesn't matter that much if you click them or press them.