Hello Michael,
I can understand the conflict you are facing, don't worry somehow it is common.
as for whether to start by 0 or 1, the most common is to start by 1 so you need to start by 1 in all cases except unless the question states otherwise.
below is a step by step on how to go through the forward pass:
1- The ES of the first activity in the path is 1. The EF of any task is its ES plus its duration minus one EF = ES + Duration - 1.
2- Now move forward to the next activity in the path. To figure out ES, take the EF of the previous task and add one. So ES = EF(of the previous activity) + 1, and EF = ES + Duration - 1.
3- If an activity has two predecessors, Which one do you use to calculate EF? use the one with the latest (larger) EF.
hope this clears your confusion.