Multiple sites mean multilple installations?

Yes, another newbie here. I have been reading all the documentation on wp.org on wordpress and haven’t found an answer yet so I thought I would try to get one here.

I get unlimited domains with my hosting company. If I want to put up 4 domains which will use WP, does that mean I need 4 different installations?

I can see where I would need 4 different SQL databases, but don’t have a clue about the installation.

Thanks very much,
Zeek