Granting is one nanopublication with one statement, in the form the role definition prescribes. On a space page it is done with the role's \"add …\" action; the form asks only for the person.

Who may grant follows the tiers: an admin may grant any role, a maintainer may grant member and observer roles, a member may grant observer roles. Observer is the one role people may take for themselves, by publishing the grant about themselves — which is how someone declares interest in a space before anyone has invited them.