Site access
Site access dictates which sites are accessible for operators. When you give explicit access to some sites for an operator, they can then access those sites, their subsites and all the chargers connected to the sites in question.
Site access can be managed under Settings > Operators for your operators.
To properly utilize site access and keeping managing access simple, please make sure that your site structure is logical. If you find yourself having to give lots of singular site accesses to operators, you may want to consider moving those sites under one parent site. After that you can just provide access to that parent site and site access is inherited to the subsites as well.
Operators with Global admin permission have access to every site no matter what site access dictates.