@Canswim 

Replacing the switch on the right is straight forward. 

The two black wires on the 'old' switch are the line and load wires. Ideally you would test which one is line with a voltage tester. The load will only have power with the switch in one position, the line will have in either position of the switch. If you do not have a tester, you can guess (I'm not being facetious - it's OK to guess here) and wire one black to the line on the HS200 and the other one to the load.You will need to use the wire nuts to connect the existing black wire in the box to the respective wire on the new switch. 

The white neutral wire wire from the HS200 ties into the White wire at the existing Wire Nut inside the box. Unscrew the but add the new switch white wire and screw the nut back on. And similarly for the Ground Green Wire - however you have no wire nut for the ground wires however so add the ground wire directly to the screw at the back of the box since you have a metal switch box - you will see the bare ground wires from the Romex cables attached to those screws. 

Then turn your breaker back on; if you have mixed up the line and load, then the pairing will not work. Simply swap them over (remember to turn the breaker off!!) 

Does that help? 

p.s. Just ignore the connection on the left switch completely - they are not at all involved. And certainly do not connect your new White Wire to that White wire on the left switch - on that switch it is not actually a neutral!!! Use the wire nut as described above.