trying to configure network for multisite

Hi there, I am using the following to setup a Multisite ecommerce solution: https://premium.wpmudev.org/forums/topic/how-to-build-your-own-etsy-like-site-using-marketpress

Section 2 states:
Both sites and user accounts can be registered.

I can't find where to set this up - can you help me?

Thanks, Kelly