Welcome. My name is ***** ***** would be glad to assist.
The connection on the bottom, with the wire stripped and wrapped around the screw along with the other one plugged into the rear is the power source.
They looped the power in and then it also leaves the box to another switch and probably another location.
What is needed, is to remove the looped wire and cut it at the loop. Strip both ends, then combine those 2 with the other wire in the back.
All of those will connect to the timers BLACK wire. That will keep power as it should be to other locations and to the timer.
Then the timers red wire will connect to the single black on the switch connected at the top of the switch for the fan.
So, again, the ones at the bottom, looped and back plugged are combined all together along with the timer black.
Let me know any clarification needed or other information,