The user access helps provide access to the site's roles which gives a user permission to view and edit the system. 

You need admin rights to give access to users.

• To set up user access, go to Administrator > Users and click the 'Setup User Access' icon on that user.
  
  
  
• Note: This only grants access to the site data, but access to the site is still required.
• The below options will be presented to you, click +Add and select the site (it can be all sites) that you want to provide access to.
  
  
  
• Tick the check boxes to give access to the user then click save.
• If You want to delete the access given to the user, click the delete icon.
• When a user selects a parent, that gives access to its children.
  
  
  
  
• User data access is similar to roles as it helps provide users with access to data from the multi sites, given that the user has been granted access to those additional sites.