If you have a qualifier that one person needs to fill, but can be done across multiple assignments, that is accomplished with group qualifiers. For example, if you have three assignments at one station, and one of the people at the station needs to be a paramedic, you could use a group Qualifier to build this. To create a group level qualifier, simply go to assignment rules and drag the assignment 'on top' of the other assignment.
The system will then look across multiple assignments to fill one role.
You build shared qualifiers the same way you build qualifiers. Then, fill them into your rules the same way you did before.