There are different ways in which you could give permissions to a user to access a set of securables.
One way would be simply grant permissions to that user. So you would do something like
GRANT SELECT ON YourTableName TO TheUserName
But that probably is not the best and most maintainable way to do it. What you should ideally do is to create a new role (or all administrative assistants, for example). Then, grant privileges to the role and add the user to that role.
Another alternative is to use an active directory group. You would have an administrative assistants group who would be a user on the database. You will grant permissions to the group.