What are those slots on the bottom?

What are those slots on the bottom for? How many of them can be covered up, like with a case, or tape to hold together a broken case, without causing harm? Normal operating conditions; the computer is not used in extra-hot conditions.

I have tried to find a photo / diagram of the bottom of my MacBook Pro 15" retina, mid-2015, but to no avail. If you can provide one, or a link, that would be much appreciated.

Thanks for helping.