Thanks Mika. That’s what I thought, but then I found the following discussion that then confused me.
https://premium.wpmudev.org/forums/topic/single-sign-on-to-all-sites-in-my-entire-wp-network
and
https://www.ads-software.com/support/topic/single-sign-on-for-subdomain
My site would have a similar set up to the second thread.
So basically if a user creates a profile on one site it will be available on all sites and once they log in they do not have to log in to each site individually, is this correct?
You mentioned a plugin, which plugin would you recommend?
Thanks for your help