Help designing site

I’m looking for some advice on how I should start building my wordpress site. I’m building a site for a snowboarding company and their sister company but we want them to be sharing the same wordpress database. I’m a little confused about how categories would fit into the picture and pages as well.

I’m thinking that pages would be the content that rarely changed like Contact, Dealers, Buy Online.

I’m really just looking for some input on how someone would go about starting this from the backend of wordpress.

Any links to tutorials, documentation, or plugins is greatly appreciated.

Thank you
-JJ