Categories, Taxonomies, SEO?

Hey,

I am relatively new to WP and still try to figure out how to best structure my website.

I am running an online tourist guide. I have a home page created with “New Page”. Then I created several other pages representing my categories (e.g. Sightseeing, Nightlife, Restaurants) using also “New Page”. In each of these categories, I then added contents through “New Post” to get somthing like this:

Home
Sightseeing
– Chruch
– Old Town
Nightlife
– Pubs
– Clubs
etc.

I was now wondering what categories and taxonomies are used for? Is it just a way to organize and group posts to be displayed? And if I don’t assign any categories or taxonomies to my posts, does that have any affect to search engine results?

I know this question might be a bit silly, but I have been trying to figure it out for quite some time now.

Thanks