Do I have to reinstall WP to create another website?

If you’re just doing 2 or 3 sites, the easiest may be to install it 2 or 3 times. You can handle maintaining 3. You’ll have to upgrade all 3 every time there’s a new upgrade.

From the many methods mentioned on the Installing Multiple Blogs documentation, the one I like is called Virtual Multi-blog or VBM.
http://striderweb.com/nerdaphernalia/features/virtual-multiblog/faq/

That’s what I’ve done to install about 10 blogs, and it works. A littel complex until you figure it out. But some other folks will recommend some of the other choices there