I need some help. I want to replace the 2 old switches, fan + light, by 2 Leviton decora 1 way switches. I am confused by the wires (see attached pics), especially by the black one that goes from one switch to the other, like a loop. Also I do not see any green/ground wire. The Leviton switch has a spot for that, I guess I should use. How to connect the wires properly? Please help. Thanks in advance for a reply.
The wire that "loops" between the two switches is the hot wire from the power source. This is the same as having a single wire with 2 pig tails that connect to each switch. Since you're replacing two single-pole single-throw (SPST) switches with two of the same types, all you need to do is replace them with the exact same wiring that currently exists. There is no hot/neutral to these switches, so as long as you connect to the two screws on each switch, you will be OK.
For the ground, in the pictures you can see the bare ground wires (with some paint on them) with a wire nut at the very back of the electrical box. You can and add in two pig-tails in order to connect to your new switches ground terminals. In your particular case, since you have a plastic electrical box, you should definitely connect this wire. If your box was metal, then the switch would be grounded just by making contact with the electrical box (assuming the box were grounded).