I need a total step by step guide to set up a multisite network.

A twenty fourteen theme was installed on my domain/hosting, impossible to open it I decided to chose a theme that I could evaluate to enable the multisite mode on.

I want to set up a multisite for a social network, and from the WPMUDEV premium theme list, there are 2 themes "Social" and "community" by buddypress to choose from, my question is:

1- can either one of them replace the theme on my domain/hosting to enable the Multisite mode? or I could use something else?
2- Are social and community: themes or plugins? it is confusing!

3- Its like,I can download and save all the plugins I need on my domain/hosting dashboard how to do that? confusing!

Can anyone send me a simple step by step guide to follow or can I pay someone to install what I need, to end my misery..

I spend too much time reading Wp and need to start building my network..And need a miracle :slight_frown:

Please help!