WF1 --> S1 --> ER
ER is a Event Raise Task, in this task you would write a simple shell command to create zero byte file via touch command after successful execution of S1.
WF2 --> EW --> S2
EW is a Event Wait Task, in this task you would place that file.
So, as soon as the 1st WF is executed successfully ER would create a zero byte file and hence that file would be available at EW and your second, i.e. WF2 will start after WF1....
Hope it helps u, vote if the ans is useful to you. there are also other options but this is much practiced.