Imagine a barycenter as a ficticious object. It's mass is the combined mass of 2 objects. It's location is the center of mass of those 2 objects. The center of mass is just the weighted average of the positions.
In reality a barycenter is not an object. It is just an empty point in space. But any object that orbits the pair of objects from a great enough distance will behave as if it is orbiting the ficticious object.
For example, let's create a 5 object system:
Star A: component 1 of the binary system. 1 Msol
Star B: component 2 of the binary system. 0.9 Msol in a tight 1AU binary orbit.
Planet Aa: Orbits star A
Planet Ba: Orbits star B
Planat ABa: Orbits the pair of stars from a distance.
File > New
Creates a 1 solar-mass star
Objects > Edit Objects
Change name to Star A and change color if you like
Object > Create Objects
Name: Star B
Color : your choice
Reference Object: Star A, leave "Barycenter" unselected
Mass: 0.9 Msol
SMA: 1 AU, a close binary system
Ecc: 0.3, moderately eccentric
Inc: 0, best to define the plane of the star orbits as the ecliptic
Size:1000000 km, this is not important
All others: not important
Press Create
This creates the binary pair. Gravity Simulator uses their combined mass when converting the orbital elements you provided into the state vectors that Gravity Simulator uses to crunch the numbers.
Objects > Create Objects
Reference Object: Star A, leave "barycenter" unchecked
Name: Planet Aa
Color : your choice
Mass : 1 Mearth, or your choice
SMA : 0.1 AU, or your choice, but keep it close to the star.
Ecc : 0, or your choice, but make sure that its apastron doesn't wander too far from the star.
Inc : 0, or your choice, but keep it low so Kozai doesn't destabalize it
Size : 12000 km, or your choice
All others: unimportant
Press Create
This creates a planet in orbit around star A. Gravity Simulator uses the combined masses of Star A and Planet Aa when converting the orbital elements you provided into the state vectors that Gravity Simulator uses to crunch the numbers.
Objects > Create Objects
Reference Object: Star B, leave "barycenter" unchecked
Name: Planet Ba
Color : your choice
Mass : 1 Mearth, or your choice
SMA : 0.1 AU, or your choice, but keep it close to the star.
Ecc : 0, or your choice, but make sure that its apastron doesn't wander too far from the star.
Inc : 0, or your choice, but keep it low so Kozai doesn't destabalize it
Size : 12000 km, or your choice
All others: unimportant
Press Create
This creates a planet in orbit around star B. Gravity Simulator uses the combined masses of Star B and Planet Ba when converting the orbital elements you provided into the state vectors that Gravity Simulator uses to crunch the numbers.
Objects > Create Objects
Reference Object: Star A, this time select "barycenter".
Name: Planet ABa
Color : your choice
Mass : 1 Mearth, or your choice
SMA : 10 AU, or your choice, but keep it far.
Ecc : 0, or your choice, but make sure that its apastron doesn't wander too far from the star.
Inc : 0, or your choice.
Size : 12000 km, or your choice
All others: unimportant
Press Create
This creates a planet in orbit around the barycenter of star A and star B. Gravity Simulator creates a ficticious object whose mass is the combined mass of Star A and Star B, and whose position is the weighted average of the position of Star A and Star B. It then uses the combined masses of the ficticous object and Planet ABa when converting the orbital elements you provided into the state vectors that Gravity Simulator uses to crunch the numbers. The ficticious object is not used in the number crunching, only in creating the object, for the purpose of computing the state vectors of the planet.
You should now have the 5-object system described above.
When viewing the system, select Star A as the focus object. Then use the F/A button on the Graphics Options interface to toggle back and forth between Floating Mode and absolute Mode. Pressing F places you in the floating mode, and the screen is centered on the system barycenter. Pressing A returns you to absolute mode and the screen is centered on Star A.
In the case of your system, all the planets orbit the pair, so you would select barycenter when creating all objects except the white dwarf.