Do I need multiple themes?

I am learning WP and I do not understand if I need a seperate theme for different parts of my website or just one. I want to have a store, social network, and classroom. If I use LearnPress, I see that there are some themes that I can purchase that include addons, etc. Can that theme be used for the entire website or do I have to use a different one for the store (woocommerce) etc?