1.
Thence means from a particular place, especially when you are giving directions about how to get somewhere. (FORMAL)
I ran straight up to Columbia County, then turned East, came down the Harlem Valley and ~ home...
ADV: usu ADV adv/prep, also ADV before v
2.
Thence is used to say that something changes from one state or condition to another. (FORMAL)
...the conversion of sunlight into heat and ~ into electricity.
ADV: usu ADV prep, also ADV before v